Bernd,
I had a nasty dropper trojan on my machine a couple of weeks ago. No idea how it got on there as normally I am very stringent on control of what gets onto my computer.
I think it was part of an old program, and because the virus software is updated daily, it started to pick up old 'viruses' even though they aren't.
It got on my nerves so much, I just saved all my data and cleaned the machine down software wise and reinstalled windows, it has been perfect ever since.
BTW, for perfect virus removal, you should always turn off system restore before doing your scan. Even though you can't restore back after you turn it back on, as the files are destroyed, it ensures that viruses are not 'trapped' in the system restore files that the virus scanner can't get to. Because if you don't do that, they are liable to pop back up again some time in the future.
For curing overheating, I usually take the comp outside and give it a good going over with a blowgun from my workshop air supply. It is amazing how much crap gets stuffed into crevises around the processor and power supply fans and cooling fins, and usually the graphics card is full of it as well if it has a fan.
John