But their most interesting attack focused on the car stereo. By adding extra code to a digital music file, they were able to turn a song burned to CD into a Trojan horse. When played on the car's stereo, this song could alter the firmware of the car's stereo system, giving attackers an entry point to change other components on the car. This type of attack could be spread on file-sharing networks without arousing suspicion, they believe. "It's hard to think of something more innocuous than a song," said Stefan Savage, a professor at the University of California.

http://www.itworld.com/security/139794/with-hacking-music-can-take-control-your-car

You can already see this in action - just look at some of the nasty maps you can put on your car via some dodgey dude off ebay - malware