It seems to have come from another web admin on the server installing a program with a security flaw or other vulnerability. Please be assured that the server is constantly being updated and regular AntiVirus scans do take place, it's just hard for any single AV program to catch all the numerous windows exploits in circulation. The recent spate of problems stems from a a trojan that inserted a java script 'exploit' into one of the redirect pages for the B1 website. Unfortunately, once the system was cleaned of the trojan the javascript remained. The affected file was cleaned by hand and write protected to prevent any further problems. There was around a 24 hours delay before the users saw any benefit from the 'disinfection(?)' whilst local cache's were cleared etc.
All should b e fine now and i apologize for any inconvenience caused.
EDIT: @ Cactus: The index.php is fine, it's the portal redirect that isn't updated when we update the VBulletin software that was infected
A few permission changes on the server and a quick lookie see later and it's all sorted
BTW, Where the hell have you been??? Its been too long- PM me and come in from the wilderness
We miss ya bud!