There's a website hack that lets any website do anything on your computer, if it can persuade you to just press F1 (Help).
All it needs is you to use Internet Explorer. You can have all your updates installed, and you can have antivirus running and fully updated, but this still works. They think it requires Windows 2000 or XP, but it's better to be safe, even if you have Vista or Windows 7.
Sometimes legitimate websites get hacked and have problems like this one, and the owner may not even know for a while.
So - don't press F1 in Internet Explorer!