From paragraph "Antivirus Marketplace", section within Facebook Security (https://www.facebook.com/security), Facebook users can download antivirus prestigious, with a free license to use for six months.
The available programs are: Norton Anti-Virus 2012, Trend Micro Titanium Security Essentials, Smart Surfing (for Mac) and McAfee.
This initiative is the result of an agreement signed by Facebook with Microsoft, TrendMicro, McAfee, Sophos y Symantec.
Facebook says in its statement that “This means that when you click on a link on our website, you will benefit not only existing protections on Facebook, but also for monitoring security corporations in”
More information on https://www.facebook.com/security