Some other sites reporting the same thing in vBulletin, this forum topic about the same thing:
Trojan Horse - Yamaha Grizzly ATV Forum
On page 3 of that topic it gives these 3 links:
Is vBulletin.com Infected by a virus ? - vBulletin.org Forum *WARNING ABOUT THESE 2 LINKS BELOW*, these are the other 2 links it gives, which I believe are the real vbulletin.com site urls, when I visited them my AVG anti virus gave a virus warning, I've broken the links to prevent accidental clicking:
http://w w w. vbulletin.com/forum/showthread.php?336457-My-vB-3-8-websites-infected-with-Trojan-Downloader-JS-Agent-ewo
http://w w w .vbulletin.com/forum/showthread.php?336433-Malicious-Software
I get no virus warning on Acorn at all, not seeing any of the stuff at the footer of the page either, I'm on Opera browser