GEN:SID 1:1163
Message WEB-CGI webdist.cgi access
Summary This event is generated when an attempt is made to exploit a known
vulnerability in a Web server running on an IRIX platform.
Impact Serious. Execution of arbitrary code is possible.
Detailed Information IRIX versions 5.0 through 6.3 contain a CGI script (/var/www/cgi-bin/webdist.cgi)
for remote administration purposes. This script, as originally released by
SGI, contains a vulnerability that can allow an attacker to run any
arbitrary command that the web server user has access to.
Affected Systems IRIX systems 5.0 to 6.3
Attack Scenarios An attacker makes a request for the script followed by a semi-colon
character ";" and then the command to be executed.
Ease of Attack Simple. No exploit software required.
Corrective Action Disallow the use of this script on the server.

Check for further signs of compromise.
Additional References  
Rule References bugtraq: 374
cve: 1999-0039
nessus: 10299