I'll blame you for virus writers who can program such things. They apparently have not thought of this yet, and there you go giving them ideas on how they should override the fans.
Doesn't really matter, though, CPUs that get too hot simply clock down or halt. So you'd be left with a PC that starts up with a fan on, the OS loads with the virus and then fans shut off. Sounds suspicious already. After that, the PC simply slows down and shuts off, just like every other worm. Nothing new or inventive here. Plus easily detected.