Guys, take note. Seems like facebook is forcing user to download install anti virus program to scan their system for malicious virus. There could be two possible reasons for this compulsory requirement. First, Facebook is genuinely concern about helping users to get rid of malicious virus. Or two, Facebook is trying to clamp down on marketers by profiling the computer identity used so that it can be easily cross reference for future facebook accounts. Once you install the antivirus program, alot of your system info can be pass on back to facebook easily without your knowledge. Seems like this is going to be tougher going forward for Facebook marketers.