Well, this doesn't sound good. In a report titled "Experimental Security Analysis of a Modern Automobile," researchers found that the electronic control units (or ECUs) found in cars such as GMC's Yukon hybrid are susceptible to tampering. So vulnerable, in fact, that they labeled them as "fragile."
An electrical control unit, if your car has one, is essentially its nerve center. It has a hand in almost all of the operations of your car performs. If it gets hacked, all of that functionality is suddenly at the hands of a puppet master.
"We are able to forcibly and completely disengage the brakes while driving, making it difficult for the driver to stop," the report stated. "Conversely, we are able to forcibly activate the brakes, forcing the driver forward and causing the car to stop suddenly."
That's not the extent of it, either. The researchers were able to access the lights, engine, air conditioning, locks and even the radio. The idea of hacking a car to gain control isn't new, exactly, but as car electronics get more complex (and not more secure), the worry is that something like this will give someone a lot of control over someone's car — and very easily.
You can read the full report for yourself here (heads up: it's a PDF download).