Free Antivirus: Comodo

Comodo are better known for their firewall but they also offer free antivirus protection. Comodo is a veteran of the game having been around since 1998 with expertise in Firewall and Antivirus protection. The Comodo companies offer many free products through their website, available for public download. Most notable of Comodo's free products is the Comodo Internet Security freeware program, incorporating Comodo's firewall, Comodo Firewall Pro, Host Intrusion Prevention System and antivirus.

Free Antivirus: Immunet

Immunet is a unique cloud based antivirus system. It is very small, fast and efficient using only around 10MB to store its ClamAV antivirus engine. All virus definition files are stored on a cloud server and are matched from the hosts pc to the server to determine whether infection has taken place or not.

Free Antivirus: Avira

Avira is very well used antivirus program, the likes of Ashampoo, Ad-Aware and Webroot Web Washer all use Avira's antivirus engine to provide their services. And obviously Avira use it to provide their own free and paid antivirus services. Avira has an impressive 100 million users at the last accurate count in 2009.