More and more of the systems in cars today are essentially small, networked computers. From the engine and transmission to turn signals and door locks, they all talk to each other and are subject to some of the same security threats facing your home or work computer. Researchers were recently able to access those systems with a specially crafted music CD which took control of the stereo, and from there jumped to the other networked systems. Some auto manufacturers are now starting to include Internet access, opening up the possibility for some very interesting remote attacks on your car.
http://www.securitynewsdaily.com/the-sound-of-hacking-researchers-use-trojan-cd-to-hack-car-0604/