Avast free Antivirus
Avast has a user friendly interface and does use much of the system resources. It has a Remote Access Assistance tool which behaves like the windows remote desktop. Avast could identify most of the malware and could complete the quick scan in just 15 mins. It is not as good as the paid version of bitdefender but is best available free antivirus. As it is a free version it is packed with ads. It supports Windows XP, 8,7 and Vista. Avast does not support Mac
Avira Free Antivirus 13
Avira is one of the fastest free antivirus softwares available but cannot detect most of the new malwares. Only a few features are usable in this version and people are tempted to upgrade to the paid version. As compared to Avast it is faster but bad test results makes it a poor software. It supports Windows 7,8,Vista and XP.
AVG Antivirus 13 free
Everyone would have heard the name of AVG. It provides decent protection better than Avira but not as good as Avast and has a massive file size of 227 MB. The user interface is inspired by the Windows 8 Tiles in the start window. It supports only Windows 7,8,Vista and XP.
Best free Antivirus software for PC 2013