there called Randomweres, their not virus in the least, as a matter of fact, the way the get in is via "regurated" sites, meaning they clone sites and make doubles of them. they lock your primary files down, most virus protecters wont notice this as its not a virus, i a remote accese that people had gained via clicking on their cloned site links
even when you think its safe, your not, system restore only makes them go dormint, i have been hit by only 2, and come to fine out i have 7 ""Sleeping"" in my systems, fun right? but ya, look up Randomwear, thats what ya got