Antivirus free download in window 7 the best

Avira
Malwarebytes - first-hand experience using it to remove pretty annoying (and undying upon any other anti-virus programs) malwares in several computers.

Both have free versions, and frees are useful enough. I have a paid version of Malwarebytes in my work desktop, which sometimes bothers me web-surfing since its real-time protection module is heuristic and gives false alarm once in a while.
 


2nd that about Microsoft Security Essentials.