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                                                                    EXHIBIT 31.1


                    CERTIFICATION OF CHIEF EXECUTIVE OFFICER

I, Thomas E. Noonan, Chief Executive Officer and President of Internet Security
Systems, Inc., certify that:

         1. I have reviewed this annual report on Form 10-K of Internet Security
Systems, Inc. ("Registrant");

         2. Based on my knowledge, this annual report does not contain any
untrue statement of a material fact or omit to state a material fact necessary
to make the statements made, in light of the circumstances under which such
statements were made, not misleading with respect to the period covered by this
annual report;

         3. Based on my knowledge, the financial statements, and other financial
information included in this annual report, fairly present in all material
respects the financial condition, results of operations and cash flows of
Registrant as of, and for, the periods presented in this annual report;

         4. Registrant's other certifying officer and I am responsible for
establishing and maintaining disclosure controls and procedures (as defined in
Exchange Act Rules 13a-15(e) and 15d-15(e)) for Registrant and have:

                  a. designed such disclosure controls and procedures , or
         caused such disclosure controls and procedures to be designed under our
         supervision, to ensure that material information relating to
         Registrant, including its consolidated subsidiaries, is made known to
         us by others within those entities, particularly during the period in
         which this annual report is being prepared;

                  b. evaluated the effectiveness of Registrant's disclosure
         controls and procedures presented in this annual report our conclusions
         about the effectiveness of the disclosure controls and procedures, as
         of the end of the period covered by this annual report based on such
         evaluation; and

                  c. disclosed in this annual report any change in Registrant's
         internal control over financial reporting that occurred during
         Registrant's fourth quarter of fiscal 2003 that has materially
         affected, or is reasonably likely to materially affect, Registrant's
         internal control over financial reporting; and

         5. Registrant's other certifying officer and I have disclosed, based on
our most recent evaluation of internal control over financial reporting, to
Registrant's auditors and the audit committee of Registrant's board of directors
(or persons performing the equivalent functions):

                  a. all significant deficiencies and material weaknesses in the
         design or operation of internal control over financial reporting which
         are reasonably likely to adversely affect Registrant's ability to
         record, process, summarize and report financial information; and

                  b. any fraud, whether or not material, that involves
         management or other employees who have a significant role in
         Registrant's internal control over financial reporting.


                                          /s/ THOMAS E. NOONAN
                                       ---------------------------------
                                       Thomas E. Noonan
                                       Chief Executive Officer and President


March 15, 2004