As of yesterday, my pc has become very infected with nasty viruses, that came in via facebook. My anti-virus softwear cant fight them, so I'm in the position now of having to get even more antivirus stuff. I'm quite annoyed to say the least. I've not had virus problems with this laptop since I had it, over a year ago. Hhrrmph.
So be warned and wary, especially on FB, dont open anything that says its a link to 'you tube'. Watch out for the spelling of it - 'yuo tube' - that dawned on me too late.
Make sure all you antivirus stuff is up to date!