Is there any malware that would rinder a computer totally useless?

Im totally sure its plausable, but who would create such a thing besides a corperation trying to get users to buy new pc's, The phishers only want your info, the hackers only want to take down corperation big bosses. Hackers get the wrong image put upon them by the media in my opinion. But to your question, if you were looking at a virus that would cause that, you could set it up to run the cpu memory and hardrive at 99 percent. That would create alot of heat destroying the innards, the scary part thats not hard to do, it can be a batch script hidden inside a picture. Then right before the hard drive dies, they add in a simple command to format the hard drive (fdisk)

Im not trying to scare you, just prepare you. I dont think you should worry as the ones with this skill do good deeds only

no not possible, modern motherboards will shutdown if the cpu or drives get too hot and you can just switch off anyway

yes. they can be found on websites with .ru extension. ru means russian website. if you download lot of stuff from .ru websites, sooner or later you will encounter such nasty virus