Meticulously overwhelming its computer networks, the hackers showed that ? given time ? they would be able to pop the trunk and start the windshield wipers, cut the brakes or lock them up, and even kill the engine.

Their motives were not malicious. These hackers worked on behalf of the U.S. military, which along with the auto industry is scrambling to fortify the cyber defenses of commercially available cars before criminals and even terrorists penetrate them.

"You're stepping into a rolling computer now," said Chris Valasek, who helped catapult car hacking into the public eye when he and a partner revealed last year they had been able to control a 2010 Toyota Prius and 2010 Ford Escape by plugging into a port used by mechanics.

These days, when Valasek isn't working his day job for a computer security firm, he's seeing how Bluetooth might offer an entry point.