When it comes to selecting the best free antivirus software, the choices are too limited to leave any of the free antivirus products out. Following is a list of the best - and often the only - free antivirus software for Windows and Mac computers.
1. Avira AntiVir Personal for Windows
Avira AntiVir Personal for Windows has an easy-to-use interface and pre-configured scan tasks to quickly scan your most important drives and folders. Right-click scans can be performed on individual files and folders in Explorer or on the desktop. Or, files can be dragged and dropped into the AntiVir console for quick scanning.
Avira AntiVir Personal can be used in Safe Mode, a definite plus for removing stubborn infectors or cleaning a system that might otherwise be unable to boot into Windows.
Runs on supported versions of Windows 2000 (server and workstation). as well as the 32-bit and 64-bit versions of the following: Windows XP, Windows Vista, Windows Server 2003, and Windows Server 2008.
2. PC Tools iAntivirus for Mac
PC Tools iAntivirus guards against Mac only malware, including viruses, worms, trojans, spyware and adware. Unlike some Mac antivirus software, PC Tools iAntivirus doesn't cover Windows-based malware, which helps keep performance costs and system impact low but may not be the best bet choice in a mixed Mac/Windows environment.
PC Tools iAntivirus is free for home (and home office) use and currently supports Intel-based Macs running OS X 10.5 only. An unobtrusive and efficient Mac antivirus software option that dedicated Mac users will want to try.
3. AVG Free Edition for Windows
AVG Free Edition is a classic, one of the longest running free antivirus packages available for Windows XP/2000/NT/ME/98. Installing only 30Mb of files and 4 running processes, AVG Free Edition is the smallest antivirus scanner we've tested and may well be the best choice for an older PC with limited system resources.
4. Avast Home Edition for Windows
In addition to standard scanning modes, Avast Home Edition also provides scans on bootup. This can greatly increase the chance of removing stubborn infectors, particularly those that use resuscitators to thwart removal attempts. Supports workstation only versions of Windows 95/98/Me, 2000, XP, and Vista.
5. ClamXav for Mac
ClamXav is based on the open source ClamAV virus scanner. Popular among open source fans, in practice ClamAV lags behind the detection capabilities of commercial antivirus software. For Mac users, this may not be a significant limitation given that there are far fewer malware impacting the Mac OS. If you're looking for free Mac antivirus software, ClamXav is certainly a virus scanner worth trying.

