Free Antivirus Software
Virus.Org Rogue File Scanning Service (Beta)
This service scans uploaded files with several common Anti-Virus tools to attempt to determine if the uploaded file is in fact some form of Malware.
BitDefender Free Online Virus Scan
This is an online virus scanner for users that have windows and internet explorer.
Jotti's malware scan
This site allows you to upload a single file and have it scanned by multiple virus scanners.
Freedom Online Virus Check
Freedom Online Virus Check is a free online anti-virus scanner for web users.
Windows Live Safety Center
This is a Microsoft beta online virus scanner for windows.
Trend Micro - Free Online Virus Scan
A free online virus scanner. This took a while to download the necessary file to do the scan, but then I have a slow dial-up connection. In any event it was free and it seemed to work well.
Panda ActiveScan
According to the website, Panda ActiveScan is a powerful online antivirus that scans your computer for viruses, free of charge, with just a simple click from your browser. (only works with internet explorer)
RAV AntiVirus Online Virus Scan
Free Online Virus Scanner.
Trojan Scan
Scan your system for trojans using this free online trojan scanner.
Advanced Port Scanner
The Advanced Port Scanner will test your system for open ports that can be used in attacks on your computer.