GEN:SID 1:1660
Message WEB-IIS trace.axd access
Summary This event is generated when an attempt is made to trace previous web requests on the vulnerable server.
Impact Information gathering.  This attack may permit viewing sensitive information such as Session ID values and the paths associated with the web requests.
Detailed Information Microsoft ASP.NET is software used for developing web applications.  It may have tracing enabled to view the previous 50 web requests to the server. At attacker may view sensitive information such as Session ID values and the paths associated withe previous web requests.
Affected Systems Attack Scenarios:
An attacker can attempt to access the traced requests to gather information.
Attack Scenarios  
Ease of Attack Easy.  
Corrective Action Set <trace enabled=false> in web.config
Additional References Nessus
http://cgi.nessus.org/plugins/dump.php3?id=10993
Rule References nessus: 10993