Can someone please explain!

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

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