avast The Best Windows Softwareavast! Free Antivirus
Expect great all-around protection against viruses and trojans.
avira The Best Windows SoftwareAntiVir Free Version
Lightweight and solid. Good ratings. Worth looking into.
AVG Antivirus Free Edition
Not as good as Avast or Avira but with considerably less bloat. The most popular free antivirus.
Microsoft Security Essentials
Simple, effective and lightweight protection suite.
Comodo Internet Security
Free security suite, includes both a firewall and anti-virus protection.
Lavasoft Ad-Aware+ Free
A complete anti-virus and anti-malware solution in one tidy free package.
Panda Cloud Antivirus Free Edition
A capable cloud-based antivirus that’s relatively light on resources with decent detection rates.
BitDefender Free Antivirus
Finally BitDefender has released a free version of their antivirus software, optimized for Windows 8.