I was using two laptops at once. The first one was sat beside me displaying facebook while I was building a website on the other.
I wasn't even touching the one with facebook on when all of a sudden my AVG anti virus pops up with a threat.
The pop up listed about 4 or 5 viruses in the AppData folder. So I just clicked 'Remove selected files' but nothing happened or changed.
My laptop suddenly went berserk, I kept getting pop-ups saying 'Application cannot open ***.exe is infected'
I just spent the last hour or so removing the virus and getting my laptop back to a normal state.

I was wondering how this virus got on my system. Like I said, the only website open at the time was Facebook and I wasn't downloading or running anything.

Any ideas?