<PAGE>   1

    As filed with the Securities and Exchange Commission on January 22, 1999

                                                 Registration No. 333-________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D. C. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                      SECURITY DYNAMICS TECHNOLOGIES, INC.
             (Exact Name of Registrant as Specified in Its Charter)

            DELAWARE                                        04-2916506
(State or Other Jurisdiction of                          (I.R.S. Employer
Incorporation or Organization)                        Identification Number)

 36 CROSBY DRIVE, BEDFORD, MASSACHUSETTS                      01730
(Address of Principal Executive Offices)                   (Zip Code)

                 1998 NON-OFFICER EMPLOYEE STOCK INCENTIVE PLAN
                            (Full Title of the Plan)

                             ARTHUR W. COVIELLO, JR.
                      SECURITY DYNAMICS TECHNOLOGIES, INC.
                                 36 CROSBY DRIVE
                          BEDFORD, MASSACHUSETTS 01730
                     (Name and Address of Agent for Service)

                                 (781) 687-7000
          (Telephone Number, Including Area Code, of Agent for Service)


<PAGE>   2



                         CALCULATION OF REGISTRATION FEE

================================================================================
                                  Proposed       Proposed       
    Title of                       Maximum        Maximum  
   Securities       Amount        Offering       Aggregate      Amount of  
     to be          to be           Price        Offering     Registration  
   Registered     Registered      Per Share        Price            Fee
   ----------     ----------      ---------      ---------    ------------
--------------------------------------------------------------------------------
Common Stock,      402,000        $24.63(1)     $9,901,260(1)    $2,753
$.01 par value     shares 
================================================================================

(1)  Estimated solely for the purpose of calculating the registration fee, and
     based on the average of the high and low prices of the Common Stock on the
     Nasdaq National Market on January 21, 1999 in accordance with Rules 457(c)
     and 457(h) under the Securities Act of 1933.
================================================================================


<PAGE>   3


PART I. INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

          The information required by Part I is included in documents sent or
given to participants in the Registrant's 1998 Non-Officer Employee Stock
Incentive Plan pursuant to Rule 428(b)(1) of the Securities Act of 1933, as
amended (the "Securities Act").

PART II. INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

     Item 3. INCORPORATION OF DOCUMENTS BY REFERENCE

          The Registrant is subject to the informational and reporting
requirements of Sections 13(a), 14 and 15(d) of the Securities Exchange Act of
1934, as amended (the "Exchange Act"), and in accordance therewith files
reports, proxy statements and other information with the Securities and Exchange
Commission (the "Commission"). The following documents, which are on file with
the Commission, are incorporated in this Registration Statement by reference:

          (1) The Registrant's latest annual report filed pursuant to Section
     13(a) or 15(d) of the Exchange Act, or the latest prospectus filed pursuant
     to Rule 424(b) under the Securities Act that contains audited financial
     statements for the Registrant's latest fiscal year for which such
     statements have been filed.

          (2) All other reports filed pursuant to Section 13(a) or 15(d) of the
     Exchange Act since the end of the fiscal year covered by the document
     referred to in (1) above.

          (3) The description of the common stock of the Registrant, $.01 par
     value per share (the "Common Stock"), contained in a registration statement
     filed under the Exchange Act, including any amendment or report filed for
     the purpose of updating such description.

          All documents subsequently filed by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all shares of Common Stock
offered hereby have been sold or which deregisters all shares of Common Stock
then remaining unsold, shall be deemed to be incorporated by reference herein
and to be part hereof from the date of the filing of such documents. Any
statement contained in a document incorporated or deemed to be incorporated by
reference herein shall be deemed to be modified or superseded for purposes of
this Registration Statement to the extent that a statement contained herein or
in any other subsequently filed document which also is or is deemed to be
incorporated by reference herein modifies or supersedes such statement. Any
statement so modified or superseded shall not be deemed, except as so modified
or superseded, to constitute a part of this Registration Statement.


                                      II-1


<PAGE>   4


     Item 4. DESCRIPTION OF SECURITIES

          Not applicable.

     Item 5. INTERESTS OF NAMED EXPERTS AND COUNSEL

          The legality of the Common Stock being offered hereby will be passed
upon for the Company by Hale and Dorr LLP, Boston, Massachusetts.

     Item 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS

          Article EIGHTH of the Registrant's Third Restated Certificate of
Incorporation, as amended (the "Restated Certificate of Incorporation"),
provides that no director of the Registrant shall be personally liable for any
monetary damages for any breach of fiduciary duty as a director, except to the
extent that the Delaware General Corporation Law prohibits the elimination or
limitation of liability of directors for breach of fiduciary duty.

          Article NINTH of the Registrant's Restated Certificate of
Incorporation provides that a director or officer of the Registrant (a) shall be
indemnified by the Registrant against all expenses (including attorneys' fees),
judgments, fines and amounts paid in settlement incurred in connection with any
litigation or other legal proceeding (other than an action by or in the right of
the Registrant) brought against him by virtue of his position as a director or
officer of the Registrant if he acted in good faith and in a manner he
reasonably believed to be in, or not opposed to, the best interests of the
Registrant, and, with respect to any criminal action or proceeding, had no
reasonable cause to believe his conduct was unlawful and (b) shall be
indemnified by the Registrant against all expenses (including attorneys' fees)
and amounts paid in settlement incurred in connection with any action by or in
the right of the Registrant brought against him by virtue of his position as a
director or officer of the Registrant if he acted in good faith and in a manner
he reasonably believed to be in, or not opposed to, the best interests of the
Registrant, except that no indemnification shall be made with respect to any
matter as to which such person shall have been adjudged to be liable to the
Registrant, unless a court determines that, despite such adjudication but in
view of all of the circumstances, he is entitled to indemnification of such
expenses. Notwithstanding the foregoing, to the extent that a director or
officer has been successful, on the merits or otherwise, including, without
limitation, the dismissal of an action without prejudice, he is required to be
indemnified by the Registrant against all expenses (including attorneys' fees)
incurred in connection therewith. Expenses shall be advanced to a director or
officer at his request, provided that he undertakes to repay the amount advanced
if it is ultimately determined that he is not entitled to indemnification for
such expenses.


          Indemnification is required to be made unless the Registrant
determines that the applicable standard of conduct required for indemnification
has not been met. In the event of a determination by the Registrant that the
director or officer did not meet the applicable standard of conduct required for
indemnification, or if the Registrant fails to make an indemnification payment
within 60 days after such payment is claimed by


                                      II-2


<PAGE>   5


such person, such person is permitted to petition the court to make an
independent determination as to whether such person is entitled to
indemnification. As a condition precedent to the right of indemnification, the
director or officer must give the Registrant notice of the action for which
indemnity is sought and the Registrant has the right to participate in such
action or assume the defense thereof.

          Article NINTH of the Registrant's Restated Certificate of
Incorporation further provides that the indemnification provided therein is not
exclusive, and provides that in the event that the Delaware General Corporation
Law is amended to expand the indemnification permitted to directors or officers
the Registrant must indemnify those persons to the fullest extent permitted by
such law as so amended.

          Section 145 of the Delaware General Corporation Law, as amended,
provides that a corporation may indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit or proceeding, whether civil, criminal, administrative or investigative
(other than an action by or in the right of the corporation) by reason of the
fact that he is or was a director, officer, employee or agent of the
corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by him in connection with such action, suit or proceeding if he acted
in good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the corporation, and, with respect to any criminal action
or proceeding, had no reasonable cause to believe his conduct was unlawful.
Section 145 further provides that a corporation similarly may indemnify any
person who was or is a party or is threatened to be made a party to any
threatened, pending or completed action or suit by or in the right of the
corporation to procure a judgment in its favor by reason of the fact that he is
or was a director, officer, employee or agent of the corporation, or is or was
serving at the request of the corporation as a director, officer, employee or
agent of another corporation, partnership, joint venture, trust or other
enterprise, against expenses (including attorneys' fees) actually and reasonably
incurred by him in connection with the defense or settlement of such action or
suit if he acted in good faith and in a manner he reasonably believed to be in
or not opposed to the best interests of the corporation, except that no
indemnification shall be made in respect of any claim, issue or matter as to
which such person shall have been adjudged to be liable to the corporation
unless and only to the extent that the Delaware Court of Chancery or the court
in which such action or suit was brought shall determine upon application that,
despite an adjudication of liability but in view of all the circumstances of the
case, such person is fairly and reasonably entitled to indemnity for such
expenses which the Court of Chancery or such other court shall deem proper.

          The Registrant has directors and officers liability insurance for the
benefit of its directors and officers.

     Item 7. EXEMPTION FROM REGISTRATION CLAIMED

          Not applicable.


                                      II-3


<PAGE>   6



     Item 8. EXHIBITS

          The Exhibit Index immediately preceding the exhibits is incorporated
herein by reference.

     Item 9. UNDERTAKINGS

          1. The undersigned Registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are being
          made, a post-effective amendment to this Registration Statement:

               (i) To include any prospectus required by Section 10(a)(3) of the
          Securities Act;

               (ii) To reflect in the prospectus any facts or events arising
          after the effective date of the Registration Statement (or the most
          recent post-effective amendment thereof) which, individually or in the
          aggregate, represent a fundamental change in the information set forth
          in the Registration Statement; and

               (iii) To include any material information with respect to the
          plan of distribution not previously disclosed in the Registration
          Statement or any material change to such information in the
          Registration Statement;

          provided, however, that paragraphs (i) and (ii) do not apply if the
     information required to be included in a post-effective amendment by those
     paragraphs is contained in periodic reports filed with or furnished to the
     Commission by the Registrant pursuant to Section 13 or 15(d) of the
     Exchange Act that are incorporated by reference in the Registration
     Statement.

          (2) That, for the purpose of determining any liability under the
     Securities Act, each such post-effective amendment shall be deemed to be a
     new Registration Statement relating to the securities offered therein, and
     the offering of such securities at that time shall be deemed to be the
     initial bona fide offering thereof.

          (3) To remove from registration by means of a post-effective amendment
     any of the securities being registered which remain unsold at the
     termination of the offering.

          2. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange
Act (and, where applicable, each filing of an employee benefit plan's annual
report pursuant to Section 15(d) of the Exchange Act) that is incorporated by
reference in the Registration Statement shall be 


                                      II-4


<PAGE>   7


deemed to be a new Registration Statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

          3. Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the Registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.


                                      II-5


<PAGE>   8


                                   SIGNATURES

          Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the Town of Bedford, Massachusetts on January 22, 1999.

                                            SECURITY DYNAMICS TECHNOLOGIES, INC.



                                            By: /s/ Charles R. Stuckey, Jr.
                                               ----------------------------
                                                  Charles R. Stuckey, Jr.
                                                  Chairman of the Board,
                                                  President and Chief
                                                  Executive Officer

                                POWER OF ATTORNEY

          We, the undersigned officers and directors of Security Dynamics
Technologies, Inc. hereby severally constitute Charles R. Stuckey, Jr., Arthur
W. Coviello, Jr., Marian G. O'Leary and Hal J. Leibowitz, and each of them
singly, our true and lawful attorneys with full power to them, and each of them
singly, to sign for us and in our names in the capacities indicated below, the
Registration Statement on Form S-8 filed herewith and any and all subsequent
amendments to said Registration Statement, and generally to do all such things
in our names and behalf in our capacities as officers and directors to enable
Security Dynamics Technologies, Inc. to comply with all requirements of the
Securities and Exchange Commission, hereby ratifying and confirming our
signatures as they may be signed by said attorneys, or any of them, to said
Registration Statement and any and all amendments thereto.


                                      II-6


<PAGE>   9


          Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.


      SIGNATURE                         TITLE                  DATE
      ---------                         -----                  ----

                                
/s/ Charles R. Stuckey, Jr.     Chairman of the Board     January 22, 1999
----------------------------    of Directors, President                      
Charles R. Stuckey, Jr.         and Chief Executive     
                                Officer (Principal      
                                Executive Officer)      
                                                        
                                                        
                                
                                          
/s/ Marian G. O'Leary           Senior Vice President,    January 22, 1999 
---------------------------     Finance, Chief Financial 
Marian G. O'Leary               Officer and Treasurer    
                                (Principal Financial and 
                                Accounting Officer)      
                                


/s/ D. James Bidzos             Director                  January 22, 1999
--------------------------
D. James Bidzos


/s/ Richard L. Earnest          Director                  January 22, 1999
--------------------------
Richard L. Earnest


/s/ Joseph B. Lassiter, III     Director                  January 22, 1999
--------------------------
Joseph B. Lassiter, III


/s/ George M. Middlemas         Director                  January 22, 1999
--------------------------
George M. Middlemas


/s/ Sanford M. Sherizen         Director                  January 22, 1999
--------------------------
Sanford M. Sherizen


/s/ James K. Sims               Director                  January 22, 1999
--------------------------
James K. Sims


                                      II-7


<PAGE>   10


                                  EXHIBIT INDEX

 Exhibit
 Number                           Description
 ------                           -----------

      4.1    Specimen Certificate of Common Stock, $.01 par value per share, of
             the Registrant is incorporated herein by reference to Exhibit 4.1 
             to the Registrant's Registration Statement on Form S-1, as amended 
             (File No. 33-85606)

      5      Opinion of Hale and Dorr LLP

     23.1    Consent of Hale and Dorr LLP (included in Exhibit 5)

     23.2    Consent of Deloitte & Touche LLP, independent auditors

     23.3    Consent of Ernst & Young LLP, independent auditors

     24      Power of Attorney (included in the signature pages of this
             Registration Statement)


                                      II-8
[{"type": "S-8", "sequence": "1", "description": "SECURITY DYNAMICS TECHNOLOGIES, INC.", "secsgml_size_bytes": 21038}]
{"company-data": {"conformed-name": "SECURITY DYNAMICS TECHNOLOGIES INC /DE/", "cik": "0000932064", "assigned-sic": "3577", "irs-number": "042916506", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-71075", "film-number": "99511681"}, "business-address": {"street1": "20 CROSBY DRIVE", "city": "BEDFORD", "state": "MA", "zip": "01730", "phone": "6176877000"}, "mail-address": {"street1": "20 CROSBY DRIVE", "city": "BEDFORD", "state": "MA", "zip": "01730"}}
1

    As filed with the Securities and Exchange Commission on January 22, 1999

                                                 Registration No. 333-________

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D. C. 20549

                                    FORM S-8

                          REGISTRATION STATEMENT UNDER
                           THE SECURITIES ACT OF 1933

                      SECURITY DYNAMICS TECHNOLOGIES, INC.
             (Exact Name of Registrant as Specified in Its Charter)

            DELAWARE                                        04-2916506
(State or Other Jurisdiction of                          (I.R.S. Employer
Incorporation or Organization)                        Identification Number)

 36 CROSBY DRIVE, BEDFORD, MASSACHUSETTS                      01730
(Address of Principal Executive Offices)                   (Zip Code)

                 1998 NON-OFFICER EMPLOYEE STOCK INCENTIVE PLAN
                            (Full Title of the Plan)

                             ARTHUR W. COVIELLO, JR.
                      SECURITY DYNAMICS TECHNOLOGIES, INC.
                                 36 CROSBY DRIVE
                          BEDFORD, MASSACHUSETTS 01730
                     (Name and Address of Agent for Service)

                                 (781) 687-7000
          (Telephone Number, Including Area Code, of Agent for Service)
2

                         CALCULATION OF REGISTRATION FEE

================================================================================
                                  Proposed       Proposed       
    Title of                       Maximum        Maximum  
   Securities       Amount        Offering       Aggregate      Amount of  
     to be          to be           Price        Offering     Registration  
   Registered     Registered      Per Share        Price            Fee
   ----------     ----------      ---------      ---------    ------------
--------------------------------------------------------------------------------
Common Stock,      402,000        $24.63(1)     $9,901,260(1)    $2,753
$.01 par value     shares 
================================================================================

(1)  Estimated solely for the purpose of calculating the registration fee, and
     based on the average of the high and low prices of the Common Stock on the
     Nasdaq National Market on January 21, 1999 in accordance with Rules 457(c)
     and 457(h) under the Securities Act of 1933.
================================================================================
3

PART I. INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS

          The information required by Part I is included in documents sent or
given to participants in the Registrant's 1998 Non-Officer Employee Stock
Incentive Plan pursuant to Rule 428(b)(1) of the Securities Act of 1933, as
amended (the "Securities Act").

PART II. INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

     Item 3. INCORPORATION OF DOCUMENTS BY REFERENCE

          The Registrant is subject to the informational and reporting
requirements of Sections 13(a), 14 and 15(d) of the Securities Exchange Act of
1934, as amended (the "Exchange Act"), and in accordance therewith files
reports, proxy statements and other information with the Securities and Exchange
Commission (the "Commission"). The following documents, which are on file with
the Commission, are incorporated in this Registration Statement by reference:

          (1) The Registrant's latest annual report filed pursuant to Section
     13(a) or 15(d) of the Exchange Act, or the latest prospectus filed pursuant
     to Rule 424(b) under the Securities Act that contains audited financial
     statements for the Registrant's latest fiscal year for which such
     statements have been filed.

          (2) All other reports filed pursuant to Section 13(a) or 15(d) of the
     Exchange Act since the end of the fiscal year covered by the document
     referred to in (1) above.

          (3) The description of the common stock of the Registrant, $.01 par
     value per share (the "Common Stock"), contained in a registration statement
     filed under the Exchange Act, including any amendment or report filed for
     the purpose of updating such description.

          All documents subsequently filed by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all shares of Common Stock
offered hereby have been sold or which deregisters all shares of Common Stock
then remaining unsold, shall be deemed to be incorporated by reference herein
and to be part hereof from the date of the filing of such documents. Any
statement contained in a document incorporated or deemed to be incorporated by
reference herein shall be deemed to be modified or superseded for purposes of
this Registration Statement to the extent that a statement contained herein or
in any other subsequently filed document which also is or is deemed to be
incorporated by reference herein modifies or supersedes such statement. Any
statement so modified or superseded shall not be deemed, except as so modified
or superseded, to constitute a part of this Registration Statement.

                                      II-1
4

     Item 4. DESCRIPTION OF SECURITIES

          Not applicable.

     Item 5. INTERESTS OF NAMED EXPERTS AND COUNSEL

          The legality of the Common Stock being offered hereby will be passed
upon for the Company by Hale and Dorr LLP, Boston, Massachusetts.

     Item 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS

          Article EIGHTH of the Registrant's Third Restated Certificate of
Incorporation, as amended (the "Restated Certificate of Incorporation"),
provides that no director of the Registrant shall be personally liable for any
monetary damages for any breach of fiduciary duty as a director, except to the
extent that the Delaware General Corporation Law prohibits the elimination or
limitation of liability of directors for breach of fiduciary duty.

          Article NINTH of the Registrant's Restated Certificate of
Incorporation provides that a director or officer of the Registrant (a) shall be
indemnified by the Registrant against all expenses (including attorneys' fees),
judgments, fines and amounts paid in settlement incurred in connection with any
litigation or other legal proceeding (other than an action by or in the right of
the Registrant) brought against him by virtue of his position as a director or
officer of the Registrant if he acted in good faith and in a manner he
reasonably believed to be in, or not opposed to, the best interests of the
Registrant, and, with respect to any criminal action or proceeding, had no
reasonable cause to believe his conduct was unlawful and (b) shall be
indemnified by the Registrant against all expenses (including attorneys' fees)
and amounts paid in settlement incurred in connection with any action by or in
the right of the Registrant brought against him by virtue of his position as a
director or officer of the Registrant if he acted in good faith and in a manner
he reasonably believed to be in, or not opposed to, the best interests of the
Registrant, except that no indemnification shall be made with respect to any
matter as to which such person shall have been adjudged to be liable to the
Registrant, unless a court determines that, despite such adjudication but in
view of all of the circumstances, he is entitled to indemnification of such
expenses. Notwithstanding the foregoing, to the extent that a director or
officer has been successful, on the merits or otherwise, including, without
limitation, the dismissal of an action without prejudice, he is required to be
indemnified by the Registrant against all expenses (including attorneys' fees)
incurred in connection therewith. Expenses shall be advanced to a director or
officer at his request, provided that he undertakes to repay the amount advanced
if it is ultimately determined that he is not entitled to indemnification for
such expenses.

          Indemnification is required to be made unless the Registrant
determines that the applicable standard of conduct required for indemnification
has not been met. In the event of a determination by the Registrant that the
director or officer did not meet the applicable standard of conduct required for
indemnification, or if the Registrant fails to make an indemnification payment
within 60 days after such payment is claimed by

                                      II-2
5

such person, such person is permitted to petition the court to make an
independent determination as to whether such person is entitled to
indemnification. As a condition precedent to the right of indemnification, the
director or officer must give the Registrant notice of the action for which
indemnity is sought and the Registrant has the right to participate in such
action or assume the defense thereof.

          Article NINTH of the Registrant's Restated Certificate of
Incorporation further provides that the indemnification provided therein is not
exclusive, and provides that in the event that the Delaware General Corporation
Law is amended to expand the indemnification permitted to directors or officers
the Registrant must indemnify those persons to the fullest extent permitted by
such law as so amended.

          Section 145 of the Delaware General Corporation Law, as amended,
provides that a corporation may indemnify any person who was or is a party or is
threatened to be made a party to any threatened, pending or completed action,
suit or proceeding, whether civil, criminal, administrative or investigative
(other than an action by or in the right of the corporation) by reason of the
fact that he is or was a director, officer, employee or agent of the
corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by him in connection with such action, suit or proceeding if he acted
in good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the corporation, and, with respect to any criminal action
or proceeding, had no reasonable cause to believe his conduct was unlawful.
Section 145 further provides that a corporation similarly may indemnify any
person who was or is a party or is threatened to be made a party to any
threatened, pending or completed action or suit by or in the right of the
corporation to procure a judgment in its favor by reason of the fact that he is
or was a director, officer, employee or agent of the corporation, or is or was
serving at the request of the corporation as a director, officer, employee or
agent of another corporation, partnership, joint venture, trust or other
enterprise, against expenses (including attorneys' fees) actually and reasonably
incurred by him in connection with the defense or settlement of such action or
suit if he acted in good faith and in a manner he reasonably believed to be in
or not opposed to the best interests of the corporation, except that no
indemnification shall be made in respect of any claim, issue or matter as to
which such person shall have been adjudged to be liable to the corporation
unless and only to the extent that the Delaware Court of Chancery or the court
in which such action or suit was brought shall determine upon application that,
despite an adjudication of liability but in view of all the circumstances of the
case, such person is fairly and reasonably entitled to indemnity for such
expenses which the Court of Chancery or such other court shall deem proper.

          The Registrant has directors and officers liability insurance for the
benefit of its directors and officers.

     Item 7. EXEMPTION FROM REGISTRATION CLAIMED

          Not applicable.

                                      II-3
6

     Item 8. EXHIBITS

          The Exhibit Index immediately preceding the exhibits is incorporated
herein by reference.

     Item 9. UNDERTAKINGS

          1. The undersigned Registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are being
          made, a post-effective amendment to this Registration Statement:

               (i) To include any prospectus required by Section 10(a)(3) of the
          Securities Act;

               (ii) To reflect in the prospectus any facts or events arising
          after the effective date of the Registration Statement (or the most
          recent post-effective amendment thereof) which, individually or in the
          aggregate, represent a fundamental change in the information set forth
          in the Registration Statement; and

               (iii) To include any material information with respect to the
          plan of distribution not previously disclosed in the Registration
          Statement or any material change to such information in the
          Registration Statement;

          provided, however, that paragraphs (i) and (ii) do not apply if the
     information required to be included in a post-effective amendment by those
     paragraphs is contained in periodic reports filed with or furnished to the
     Commission by the Registrant pursuant to Section 13 or 15(d) of the
     Exchange Act that are incorporated by reference in the Registration
     Statement.

          (2) That, for the purpose of determining any liability under the
     Securities Act, each such post-effective amendment shall be deemed to be a
     new Registration Statement relating to the securities offered therein, and
     the offering of such securities at that time shall be deemed to be the
     initial bona fide offering thereof.

          (3) To remove from registration by means of a post-effective amendment
     any of the securities being registered which remain unsold at the
     termination of the offering.

          2. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange
Act (and, where applicable, each filing of an employee benefit plan's annual
report pursuant to Section 15(d) of the Exchange Act) that is incorporated by
reference in the Registration Statement shall be 

                                      II-4
7

deemed to be a new Registration Statement relating to the securities offered
therein, and the offering of such securities at that time shall be deemed to be
the initial bona fide offering thereof.

          3. Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the Registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

                                      II-5
8

                                   SIGNATURES

          Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the Town of Bedford, Massachusetts on January 22, 1999.

                                            SECURITY DYNAMICS TECHNOLOGIES, INC.

                                            By: /s/ Charles R. Stuckey, Jr.
                                               ----------------------------
                                                  Charles R. Stuckey, Jr.
                                                  Chairman of the Board,
                                                  President and Chief
                                                  Executive Officer

                                POWER OF ATTORNEY

          We, the undersigned officers and directors of Security Dynamics
Technologies, Inc. hereby severally constitute Charles R. Stuckey, Jr., Arthur
W. Coviello, Jr., Marian G. O'Leary and Hal J. Leibowitz, and each of them
singly, our true and lawful attorneys with full power to them, and each of them
singly, to sign for us and in our names in the capacities indicated below, the
Registration Statement on Form S-8 filed herewith and any and all subsequent
amendments to said Registration Statement, and generally to do all such things
in our names and behalf in our capacities as officers and directors to enable
Security Dynamics Technologies, Inc. to comply with all requirements of the
Securities and Exchange Commission, hereby ratifying and confirming our
signatures as they may be signed by said attorneys, or any of them, to said
Registration Statement and any and all amendments thereto.

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9

          Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.

      SIGNATURE                         TITLE                  DATE
      ---------                         -----                  ----

                                
/s/ Charles R. Stuckey, Jr.     Chairman of the Board     January 22, 1999
----------------------------    of Directors, President                      
Charles R. Stuckey, Jr.         and Chief Executive     
                                Officer (Principal      
                                Executive Officer)      
                                                        
                                                        
                                
                                          
/s/ Marian G. O'Leary           Senior Vice President,    January 22, 1999 
---------------------------     Finance, Chief Financial 
Marian G. O'Leary               Officer and Treasurer    
                                (Principal Financial and 
                                Accounting Officer)      
                                

/s/ D. James Bidzos             Director                  January 22, 1999
--------------------------
D. James Bidzos

/s/ Richard L. Earnest          Director                  January 22, 1999
--------------------------
Richard L. Earnest

/s/ Joseph B. Lassiter, III     Director                  January 22, 1999
--------------------------
Joseph B. Lassiter, III

/s/ George M. Middlemas         Director                  January 22, 1999
--------------------------
George M. Middlemas

/s/ Sanford M. Sherizen         Director                  January 22, 1999
--------------------------
Sanford M. Sherizen

/s/ James K. Sims               Director                  January 22, 1999
--------------------------
James K. Sims

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                                  EXHIBIT INDEX

 Exhibit
 Number                           Description
 ------                           -----------

      4.1    Specimen Certificate of Common Stock, $.01 par value per share, of
             the Registrant is incorporated herein by reference to Exhibit 4.1 
             to the Registrant's Registration Statement on Form S-1, as amended 
             (File No. 33-85606)

      5      Opinion of Hale and Dorr LLP

     23.1    Consent of Hale and Dorr LLP (included in Exhibit 5)

     23.2    Consent of Deloitte & Touche LLP, independent auditors

     23.3    Consent of Ernst & Young LLP, independent auditors

     24      Power of Attorney (included in the signature pages of this
             Registration Statement)

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