There is an instance out there that 'floats' around. It never stays in one spot for very long. I've yet to figure out exactly how it works but it's devastating to your machine. Essentially it 'installs' itself directly to your machine. It's usually called Anti Virus Software or some similar iteration. It looks and feels authentic but it locks your system up tighter than a drum. Getting rid of it is fairly simple if you know your way around your computer and you know how to get into safe mode. It usually installs itself into your programs directory under a folder that's named with a multitude of various letters and numbers, example "gfidkl3se." All you need to do is delete the folder and it's contents. I've read around and seen instances of registry entries needing be deleted, but I've never personally experienced the need to edit the registry. Just an FYI, and to be honest there's no way to "block" this attack. It slips right past AVG, and Norton.