Recently facebook has announced that they are allowing each facebook user to download the free full version of antivirus valid for 6 months, they have taken the initiative as a security measure for all facebook users, so this way you can get the free copy of popular antivirus like Norton, McAfee, Microsoft Security Essentials, Shophos Anti Virus and Trend Micro.
Please Note: Each facebook user can download one antivirus of user choice one time, each antivirus comes with a license of 6 months with free virus definition update during that time. Only one anti-virus software download is allowed for each facebook account. So make sure you select the anti-virus software is which would best as per your computer, as you cant change your choice later.
The AV Marketplace enables people to download six-month licenses to full versions of anti-virus software at no charge from Microsoft, McAfee, TrendMicro, Sophos, or Symantec. Facebook’s global community can now download for free powerful software to protect their computers from current and future viruses, and content security threats providing hundreds of millions of people free access to anti-virus software.
Download these Free Antivirus For Free from Facebook at this page
[ Via Facebook Security Update ]