GEN:SID 1:973
Message WEB-IIS *.idc attempt
Summary This event is generated when an attempt is made to exploit a buffer overflow associated with a file with a .idc extension.
Impact Remote access.  This attack may permit the execution of arbitrary commands on the victim server.
Detailed Information Microsoft Internet Information Service (IIS) supports files extensions including .idc that call the ISM.DLL.  A buffer overflow vulnerability exists in ISM.DLL code when it receives a malformed request, permitting the execution of arbitrary code.  
Affected Systems IIS 4.0 hosts
Attack Scenarios An attacker can send a malformed request of a .idc file that causes a buffer overflow.
Ease of Attack Simple.  Exploit code is freely available.
Corrective Action Upgrade to a more current version of IIS.
Additional References CVE
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-1999-0874

Bugtraq:
http://www.securityfocus.com/bid/307
Rule References bugtraq: 1448
cve: 1999-0874
cve: 2000-0661