Help on the meaning of the Message Audit Logs's Verdict and Action

Hello,

When I filtered the message audit logs for Sender with email address, I got the followings:

Verdict: Bounce attack signature present, Content Filtering violation: 25. Insert annotation: Anti-virus - 31MAR11-1600

Action: Add annotation, Bounce attack signature added

What does above information mean? I'm not sure...please help

Thanks,

Kim