There is a huge number of Antivirus software vendors on the market today. With every version their customer base shifts based on software' performance.

Most important things to to consider when purchasing or installing antivirus are:

• How much of your computer's resources are you allocated towards the antivirus software?
• Is it running in real-time or do you have to manually or automaticaly run file scan at scheduled intervals?
• Does it have spyware protection?
• What about pop-up blocker?
• Does it have Email protection for most popular email clients?
• What about Internet Browser filtering such as phishing? Which Web Browsers: Internet Explorer, Mozilla FireFox, Chrome, Safari, etc.
• read the latest Antivirus reviews

Downloads

http://www.microsoft.com/Security_Essentials/
Microsoft Antivirus
Avast Antivirus
Avira Antivir