Is it possible to remotely access a wireless products such a bluetooth, On-Star, GPS in vehicles?

Could it be possible that a internet hacker can access and control a vehicle's PCM module, acceleration and brake control, anit-lock breaks, unlocking the car? Several months ago China's colleges hacked was trying to hack into the Pentagon, could they have actually hacked into a Toyota's electronic system? If On-Star can unlock and start a vehicle so can anyone else that knows the components..Food Thought!!!