Well the attack wasn't from the RPF itself... But it could have been linked... Was it a particular thread you where viewing?
Have you checked your system? Might be a good time for a full system scan as that 'attack' could also be a result of some already installed malware attempting to phone home, and the AV intercepting the call...
It should be taken serious and a routine scan should be done on your system, just the same...
FYI: A little nosing around revealed that what your AV blocked was a Java exploit on that site that installs a Rootkit, pretty serious stuff as that Rootkit could be anything...