http://www.trendmicro.com/en/home/us/enterprise.htm
Click on "Free Online Scan".
I had a problem for awhile. Everything was starting to lock up on me. Norton Antivirus was run on a weekly basis and never found anything.
Was told to hit that site and did. Total result... I had 56 of the same virus on my computer. It would copy itself, because of all the times that I used System Restore.
I had to reformat everything. It was a pain in the butt, but I've basically been virus free since then.
Good Luck