Free Anti virus

Antivirus is now a days the most important software after the operating system. There are millions of viruses trying to infect your PC when you connect to internet. The Best way to protect from viruses , trojans , phishing sites etc is to use a Licensed Antivirus ( Preferably an Internet Security).
Unlike others software antivirus license are sold for only a limited time period and after that you have to again repurchase it( They call it License renewal). But there are really a few good antivirus available in the internet which can be used for free. Some of them are

i) avast : This is the most promising antivirus available for free personal use. You need to
register in the site to get a license key of 1 year.

ii) avg : This is one of the most trusted antivirus software.

Other than antivirus it is desirable that your PC has a good Antispyware software installed
Spyware terminator is really the best free anti spyware software.