So dozens of visitors to the rivals.com Penn State football board became infected with the Security Tool virus (not me!). Most, if not all, claim they had their anti-virus running and there doesn't seem to be any correlation as to any link they opened. How could that have happened?

Apparently they have a forum where they discuss this in several threads: http://bwi.rivals.com/forum.asp?fid=36

that is where I read about it, however, there isn't any explanation as to the actual source or why their anti-malwares failed.

This article by Tony Klein is very famous, "So how did I get infected in the first place?". Link: http://www.landzdown.com/index.php?topic=2783.0