content: <PAGE>   1
                As filed with the Securities and Exchange Commission
                                  on July 26, 1996
  ===============================================================================
  
                         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 No.)
  
                ONE ALEWIFE CENTER, CAMBRIDGE, MASSACHUSETTS  02140
              (Address of Principal Executive Offices)     (Zip Code)
  
                               1994 STOCK OPTION PLAN
                              (Full title of the plan)
  
                              CHARLES R. STUCKEY, JR.
                        SECURITY DYNAMICS TECHNOLOGIES, INC.
                                 ONE ALEWIFE CENTER
                           CAMBRIDGE, MASSACHUSETTS 02140
                      (Name and address of agent for service)
  
                                   (617) 547-7820
           (Telephone number, including area code, of agent for service)
  
  <TABLE>
  <CAPTION>
  - --------------------------------------------------------------------------------
                          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
  - ----------        ----------      ---------       ---------        ------------
  <S>                <C>            <C>           <C>                <C>
  Common Stock,      2,110,000      $58.375(1)    $123,171,250(1)    $42,473.00
  $.01 par           shares
  value
  - --------------------------------------------------------------------------------
  </TABLE>
  
  (1)  Estimated solely for the purpose of calculating the registration fee, and
       based upon the average of the high and low prices of the Common Stock on
       the Nasdaq National Market on July 24, 1996 in accordance with Rules 457(c)
       and 457(h) of the Securities Act of 1933.
  
  ===============================================================================
  <PAGE>   2
  PART I.   INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS
  
       The information required by Part I of Form S-8 is included in documents
  sent or given to participants in the 1994 Stock Option Plan of Security Dynamics
  Technologies, Inc., a Delaware corporation (the "Registrant"), 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
  
  Statement of Incorporation by Reference
  
       Except as otherwise set forth below, this Registration Statement on Form
  S-8 incorporates by reference the contents of the Registration Statement on Form
  S-8, File No. 33-88506 (the "Initial Registration Statement"), relating to the
  Registrant's 1994 Stock Option Plan.
  
       Item 3 of the Initial Registration Statement is amended and restated in its
  entirety as follows:
  
  Item 3.   Incorporation of Certain 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 following documents, which are filed with the Securities and Exchange
  Commission, are incorporated in this Prospectus 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 of 1933 (as amended, 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, par value $.01 per share
       ("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
  
  
                                        -2-
  
  <PAGE>   3
  incorporated by reference herein and to be part hereof from the date of the
  filing of such documents.
  
       Item 9 of the Initial Registration Statement is amended and restated in its
  entirety as follows:
  
  Item 9.   Undertakings.
  
       1.   The Company hereby undertakes.
  
            (a)  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
       registration statement is on Form S-3 or Form S-8, and the information
       required to be included in a post-effective amendment by those paragraphs
       is contained in periodic reports filed by the Company pursuant to Section
       13 or Section 15(d) of the Exchange Act that are incorporated by reference
       in the registration statement.
  
            (b)  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.
  
            (c)  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 Company hereby undertakes that, for purposes of determining any
  liability under the Securities Act, each filing of the Company's annual report
  pursuant to Section 13(a) or Section 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
  
  
  
                                        -3-
  
  <PAGE>   4
  Act) that is incorporated by reference in the registration statement 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
  in 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 Securities and Exchange
  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.
  
  
                                        -4-
  
  <PAGE>   5
                                     SIGNATURES
  
       Pursuant to the requirements of the Securities Act of 1933, 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 City of Cambridge, Commonwealth of Massachusetts on the
  26th day of July, 1996.
  
  
                                          SECURITY DYNAMICS TECHNOLOGIES, INC.
  
  
  
                                          By:/s/ Charles R. Stuckey, Jr.
                                             ---------------------------------
                                             Charles R. Stuckey, Jr.
                                             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. and Hal J. Leibowitz, Esq., 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.
  
  
                                        -5-
  
  <PAGE>   6
  
         Pursuant to the requirements of the Securities Act of 1933, this
    Registration Statement has been signed below by the following persons in the
    capacities and on the date indicated.
  
  
  Signature                            Title                    Date
  - ---------                            -----                    ----
  
  /s/ Charles R. Stuckey, Jr.      President, Chief        )
  - ---------------------------      Executive Officer       )
  Charles R. Stuckey, Jr.          and Director            )
                                   (Principal Executive    )
                                    Officer)               )
                                                           )
                                                           )
  /s/ Arthur W. Coviello, Jr.      Executive Vice President)   
  - ---------------------------      Treasurer and Chief     )
  Arthur W. Coviello, Jr.          Financial Officer       )
                                   (Principal Financial    )
                                   and Accounting Officer) )
                                                           )
                                                           )
  /s/ Richard L. Earnest           Director                )  
  - ---------------------------                              )
  Richard L. Earnest                                       )
                                                           )
                                                           )
  /s/ George M. Middlemas          Director                ) July 26, 1996
  - ---------------------------                              )
  George M. Middlemas                                      )
                                                           )
                                                           )
  /s/ Marino R. Polestra           Director                )
  - ---------------------------                              )
  Marino R. Polestra                                       )
                                                           )
                                                           )
  /s/ Sanford M. Sherizen          Director                )
  - ---------------------------                              )
  Sanford M. Sherizen                                      )
                                                           )
                                                           )
                                   Director                ) 
  - ---------------------------                              )
  Joseph Lassiter                                          )
  
                                        -6-
  
  <PAGE>   7
                                   Exhibit Index
  
  
  Exhibit
  Number       Description
  - -------      -----------
  
   4.1         Third Restated Certificate of Incorporation of the Registrant is
               incorporated herein by reference to Exhibit 4.1 to the Registrant's
               Registration Statement on Form S-8 (File No. 33-87916).
  
   4.2         Amended and Restated By-Laws of the Registrant are incorporated
               herein by reference to Exhibit 3.3 to the Registrant's Registration
               Statement on Form S-1, as amended (File No. 33-85606) (the "Form
               S-1").
  
   4.3         Specimen Certificate of Common Stock of the Registrant is
               incorporated herein by reference to Exhibit 4.1 to the Form S-1.
  
   5           Opinion of Hale and Dorr.
  
  23.1         Consent of Hale and Dorr (included in Exhibit 5).
  
  23.2         Consent of Deloitte & Touche LLP.
  
  24.1         Power of Attorney (included in the signature pages of this
               Registration Statement).
  
  
                                        -7-
metadata_documents: [{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 14753}]
metadata_filer: {"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": "333-08939", "film-number": "96599562"}, "business-address": {"street1": "ONE ALEWIFE CENTER", "city": "CAMBRIDGE", "state": "MA", "zip": "02140", "phone": "6175477820"}}
text: 1
                As filed with the Securities and Exchange Commission
                                  on July 26, 1996
  ===============================================================================
  
                         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 No.)
  
                ONE ALEWIFE CENTER, CAMBRIDGE, MASSACHUSETTS  02140
              (Address of Principal Executive Offices)     (Zip Code)
  
                               1994 STOCK OPTION PLAN
                              (Full title of the plan)
  
                              CHARLES R. STUCKEY, JR.
                        SECURITY DYNAMICS TECHNOLOGIES, INC.
                                 ONE ALEWIFE CENTER
                           CAMBRIDGE, MASSACHUSETTS 02140
                      (Name and address of agent for service)
  
                                   (617) 547-7820
           (Telephone number, including area code, of agent for service)
  - --------------------------------------------------------------------------------
                          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,      2,110,000      $58.375(1)    $123,171,250(1)    $42,473.00
  $.01 par           shares
  value
  - --------------------------------------------------------------------------------
  (1)  Estimated solely for the purpose of calculating the registration fee, and
       based upon the average of the high and low prices of the Common Stock on
       the Nasdaq National Market on July 24, 1996 in accordance with Rules 457(c)
       and 457(h) of the Securities Act of 1933.
  
  ===============================================================================
  2
  PART I.   INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS
  
       The information required by Part I of Form S-8 is included in documents
  sent or given to participants in the 1994 Stock Option Plan of Security Dynamics
  Technologies, Inc., a Delaware corporation (the "Registrant"), 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
  
  Statement of Incorporation by Reference
  
       Except as otherwise set forth below, this Registration Statement on Form
  S-8 incorporates by reference the contents of the Registration Statement on Form
  S-8, File No. 33-88506 (the "Initial Registration Statement"), relating to the
  Registrant's 1994 Stock Option Plan.
  
       Item 3 of the Initial Registration Statement is amended and restated in its
  entirety as follows:
  
  Item 3.   Incorporation of Certain 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 following documents, which are filed with the Securities and Exchange
  Commission, are incorporated in this Prospectus 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 of 1933 (as amended, 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, par value $.01 per share
       ("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
  
                                        -2-
  3
  incorporated by reference herein and to be part hereof from the date of the
  filing of such documents.
  
       Item 9 of the Initial Registration Statement is amended and restated in its
  entirety as follows:
  
  Item 9.   Undertakings.
  
       1.   The Company hereby undertakes.
  
            (a)  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
       registration statement is on Form S-3 or Form S-8, and the information
       required to be included in a post-effective amendment by those paragraphs
       is contained in periodic reports filed by the Company pursuant to Section
       13 or Section 15(d) of the Exchange Act that are incorporated by reference
       in the registration statement.
  
            (b)  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.
  
            (c)  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 Company hereby undertakes that, for purposes of determining any
  liability under the Securities Act, each filing of the Company's annual report
  pursuant to Section 13(a) or Section 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
  
                                        -3-
  4
  Act) that is incorporated by reference in the registration statement 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
  in 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 Securities and Exchange
  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.
  
                                        -4-
  5
                                     SIGNATURES
  
       Pursuant to the requirements of the Securities Act of 1933, 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 City of Cambridge, Commonwealth of Massachusetts on the
  26th day of July, 1996.
  
                                          SECURITY DYNAMICS TECHNOLOGIES, INC.
  
                                          By:/s/ Charles R. Stuckey, Jr.
                                             ---------------------------------
                                             Charles R. Stuckey, Jr.
                                             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. and Hal J. Leibowitz, Esq., 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.
  
                                        -5-
  6
  
         Pursuant to the requirements of the Securities Act of 1933, this
    Registration Statement has been signed below by the following persons in the
    capacities and on the date indicated.
  
  Signature                            Title                    Date
  - ---------                            -----                    ----
  
  /s/ Charles R. Stuckey, Jr.      President, Chief        )
  - ---------------------------      Executive Officer       )
  Charles R. Stuckey, Jr.          and Director            )
                                   (Principal Executive    )
                                    Officer)               )
                                                           )
                                                           )
  /s/ Arthur W. Coviello, Jr.      Executive Vice President)   
  - ---------------------------      Treasurer and Chief     )
  Arthur W. Coviello, Jr.          Financial Officer       )
                                   (Principal Financial    )
                                   and Accounting Officer) )
                                                           )
                                                           )
  /s/ Richard L. Earnest           Director                )  
  - ---------------------------                              )
  Richard L. Earnest                                       )
                                                           )
                                                           )
  /s/ George M. Middlemas          Director                ) July 26, 1996
  - ---------------------------                              )
  George M. Middlemas                                      )
                                                           )
                                                           )
  /s/ Marino R. Polestra           Director                )
  - ---------------------------                              )
  Marino R. Polestra                                       )
                                                           )
                                                           )
  /s/ Sanford M. Sherizen          Director                )
  - ---------------------------                              )
  Sanford M. Sherizen                                      )
                                                           )
                                                           )
                                   Director                ) 
  - ---------------------------                              )
  Joseph Lassiter                                          )
  
                                        -6-
  7
                                   Exhibit Index
  
  Exhibit
  Number       Description
  - -------      -----------
  
   4.1         Third Restated Certificate of Incorporation of the Registrant is
               incorporated herein by reference to Exhibit 4.1 to the Registrant's
               Registration Statement on Form S-8 (File No. 33-87916).
  
   4.2         Amended and Restated By-Laws of the Registrant are incorporated
               herein by reference to Exhibit 3.3 to the Registrant's Registration
               Statement on Form S-1, as amended (File No. 33-85606) (the "Form
               S-1").
  
   4.3         Specimen Certificate of Common Stock of the Registrant is
               incorporated herein by reference to Exhibit 4.1 to the Form S-1.
  
   5           Opinion of Hale and Dorr.
  
  23.1         Consent of Hale and Dorr (included in Exhibit 5).
  
  23.2         Consent of Deloitte & Touche LLP.
  
  24.1         Power of Attorney (included in the signature pages of this
               Registration Statement).
  
                                        -7-