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                                                                    EXHIBIT 31.1

                                  CERTIFICATION

I, Thomas E. Noonan, certify that:

         1.       I have reviewed this quarterly report on Form 10-Q of Internet
                  Security Systems, Inc.;

         2.       Based on my knowledge, this quarterly 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
                  quarterly report;

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

         4.       The registrant's other certifying officer and I are
                  responsible for establishing and maintaining disclosure
                  controls and procedures (as defined in Exchange Act Rules
                  13a-14 and 15d-14) for the registrant and we 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 the registrant, including its consolidated subsidiaries, is
                  made known to us by others within those entities, particularly
                  during the period in which this quarterly report is being
                  prepared;

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

                  c) disclosed in this quarterly report any change in the
                  registrant's internal control over financial reporting that
                  occurred during the registrant's most recent fiscal quarter
                  that has materially affected, or is reasonably likely to
                  materially affect, the registrant's internal control over
                  financial reporting; and

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

                  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 the
                  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
                  the registrant's internal control over financial reporting;
                  and

Date: August 8, 2003                            /s/  Thomas E. Noonan
                                                --------------------------------
                                                Thomas E. Noonan
                                                Chairman, President and
                                                  Chief Executive Officer


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