I shake at this one very horrible virus. it's hit three times, and there is no antivirus we have found that is able to pick it up or get rid of it.
It's a false antivirus pretending to be a windows program. It then starts listing of a whole bunch of pretend viruses, and then starts stopping you from opening programs by saying they are viruses, even the antivirus is a virus. Then it starts putting up websites of it's own accord, because it is there to shutdown the firewall and stop you using your antivirus, and then lets all these other viruses on using these websites. And sooner or later there is nothing at all you can do with the computer.
Luckily, it hides in the temporary folders, so all you have to do is leave the computer shut off for about a week or more and it just goes away.