Facebook, and Anti virus?

[starkillavintage]

so my computer when i go to log onto facebook is a black screen with a red backgound saying

Restricted Site This web site is restricted based on your security preferences. Your system is infected. Please activate your antivirus software.


I have norton and have been running scans all day and it doesnt say anything about being infected... can someone help me please!!!
yea it says restricted site... i download the first repliers thing and its running right now... thank you. i am so frustrated right now.. my 8 year plays farmville and all those things and i keep telling her not to cause i know they cause viruses... well i came home, and the sitter let her play them.... i dont even know how she got my password...