AVG Anti-Virus Free Edition
AVG Free Edition is the well-known anti-virus protection tool. AVG Free is available free-of-charge to home users for the life of the product! Rapid virus database updates are available for the lifetime of the product.

Avast Home Edition
avast! 4 Home Edition is a full-featured antivirus package designed exclusively for home users, non-commercial users. The Home Edition is FREE of charge.

ClamWin
ClamAV is probably the most well know open source antiivruse engine. ClamWin is a Free Antivirus for Microsoft Windows 98/Me/2000/XP/2003.

BitDefender Free Edition

BitDefender Free Edition is another great antivirus software package. It is very customizable and easy to use. Available for Windows and Linux.

AntiVir Personal Edition
The AntiVir Personal Edition offers the effective protection against computer viruses for the individual and private use on a single PC-workstation. The private and individual use of the AntiVir Personal Edition is completely free of charge! Available for Windows, Linux, OpenBSD, FreeBSD and Solaris.

Trend Micro - Online Virus Scanner
If your computer is all messed up and you need to scan it for viruses, try using Trend Micro's FREE online virus scanner.

Panda Active Scan - Online Virus Scanner
Panda Software offers a free online virus scanner. This online scanner will detect viruses and spyware on your computer.