[TheLastSuperman]

Normally I would say:
If the site was hacked, they may have edited style templates and/or files. With hooks disabled as Dave inquired about above normally any mods/plugins affected won't work so it must be either in a template or an actual vBulletin file (compromised etc).

In your case since you've tried the default style, disabled plugins, and replaced files with 100% default files then as the message states "the site had hyperlink from infected external URL" so that means you have a URL on your forum which leads to an infected site then it continues to state it's causing the false-positive detection. So with all that being said and re-iterated... what is on this page? http://projectbodybuilding.com/forum...4-Bodybuilding <-- Some link on that page is the issue, it could be an ad (I did not see ads as I had Ghostery, NoScript, and Ad Block Plus enabled when I ignored the warning and visited the site) so be sure to check and find out which link is the issue and remove it to remove the warning.

Edit:
I changed your thread title from: Same thread ID to: Site warning from infected external URL so it could be easily interpreted and searched easier.