Searching for just that domain on Google turns up a lot or results about it being related to a trojan it seems.  I would recommend following the steps provided here:

http://wiki.lunarpages.com/Web_Site_Security_Breaches

Do you have backups?  If so you might be able to roll back to a version without the exploit in place, or you might discuss your restore options with our support team at support@lunarpages.com.

Well, would depend on how bad it was, and when you were infected.  I would check on the backup status first, to see if you have a backup that would be before this got started.  What type of forum software do you use, and are you using the latest version?

If you can, try to delete the code from your forums.  Next, you might want to run a full security scan on your own PC to make sure you are not infected yourself.  Your site might be also infected because your local PC have some virus which can grab stored passwords from your FTP client software and to do login to your sites saved there and upload there viruses.

Also, looks like you are now using the latest version of vBulletin 3.8.2, which is good.  You'll also want to update your account passwords once you are sure your PC is clean or from a PC that is not infected.  Once again, I would recommend checking out this post (http://wiki.lunarpages.com/Web_Site_Security_Breaches)

Your PC anti-virus program can only scan for things on your computer, and not on the server side.  Here's another good site I found that relates to this issue:

http://blog.unmaskparasites.com/2009/05/07/gumblar-cn-exploit-12-facts-about-this-injected-script/

You will need to find the locations where the code causing this warning comes from, and remove it.  Might try right-clicking on one of your pages, and select "view page source".  Then start looking for anything that might be out of the ordinary.