Free Antivirus Software
Jotti's malware scan
This site allows you to upload a single file and have it scanned by multiple virus scanners.
BitDefender Free Online Virus Scan
This is an online virus scanner for users that have windows and internet explorer.
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.
Advanced Port Scanner
The Advanced Port Scanner will test your system for open ports that can be used in attacks on your computer.