Kaspersky: Free Online Virus Scan, this is probably the best online scanner to find out where the virus is hiding on your computer, but it will not remove the virus for you it will only tell you where it is so you can proceed will manual removal. If you are not confortable with this please use Trendmicro scanner.

Trend Micro: Free Online Virus Scan, This one is very close to Kaspersky but their free service will also remove the virus from your computer, it will also tell you your system vulnerabilities (usually missing windows updates and Security patches!).

NOD32: Free 30 day trial, this is simply the best program to find a viruses in real time, is the fastest and most efficient anti-malware program. From all antivirus software that I tested this one is the lightest (takes less RAM to operate) and the fastest scanning engine.

BitDefender: (NEW) Free Online Virus Scanner BitDefender Online Scanner is a fully functional antivirus product. It features all required elements for thorough antivirus scanning and cleaning: it scans your system's memory, all files, folders and drives' boot sectors, providing you with the option to automatically clean the infected files.

WindowSecurity: Free Oline Trojan Scanner. This program focuses specificatly on trojan viruses. If you suspect that you have been infected with a trojan virus then you could use this free scanner. A Trojan is a program that enters your computer undetected, giving the attacker who planted the Trojan unrestricted access to the data stored on your computer. Trojans can transmit credit card information and other confidential data in the background. Trojans are often not caught by poor virus scanning engines like Norton or McAfee, because these are focused on viruses, not Trojans. Catching such threats would require the use of a Trojan scanner (a.k.a Trojan cleaner, Trojan remover, anti-Trojan).