Not actually too difficult. There are a few viruses and worms around that do the trick, if you're unlucky and they bite you on the right day.
But if music companies actually go about writing malware, it will sure be interesting to watch the retaliation ;).
There are a few BIOS viruses which re-program the system BIOS to junk. That will screw up a computer, especially one with an old mother board (more than a year or two old) where the BIOS chip is hard to find or unreasonably expensive.
Forgetting about the political firestorm for the moment, there are technical ways around it. For one thing, Giga-byte touts its "Dual BIOS" technology -- they have two BIOS chips on the board, and if one gets fouled up, the other one takes over, and you can do a backup flash to get them both straightened out. I think other manufacturers would quickly come up with equivalent schemes, such as flash from disk to recover a trashed BIOS.