Virus Scan

BitDefender Online Scan Online Anti-Virus Scan from BitDefender (Much Effective)
DrWeb online virus check DrWeb online virus check (single file scan only)
Eicar Virus Test File Eicar.org will allow you to download eicar files which your antivirus program should detect.
eTrust
F-Secure Online Virus Scanner
Freedom Online Virus Check Free virus scan. It is using Command Software System
TrendMicro IE Housecall A free service from TrendMicro to scan the system for malware. This requires Internet Explorer only.
Kaspersky Online Virus Scanner Kaspersky Online Virus Scanner (Single File scan only)
Panda Active Scan Free online Anti-virus Scan from Panda (Most Effective)
PC Pitstop virus scanner
RAV Scan Online
Symantec Security Check
Trend Micro - Housecall Ease your mind and scan your PC for viruses. Supports IE, Mozilla, Netscape, Opera and Firefox!
VirusTotal Virustotal offers a free service of suspicious file scanning, using several antivirus engines.