possibilities for hackers. here's abc's chief business correspondent rebecca jarvis. >> reporter: an alarming new report from a u.s. senator finding millions of cars and trucks on the road could be at risk of hack attacks. watch as chuck gowdy of our chicago station wls demonstrates how a technology expert takes control of his car through this computer port. >> now the engine's shut off. >> you were able to do that with one mouse click. >> yes. >> reporter: the windshield wipers, the speedometer out of the driver's control. >> so can i start it? >> i don't know. can you? you can start it now. >> you did that? >> yea. >> reporter: experts say a hacker could even turn some cars into oncoming traffic, although it hasn't happened yet. the warning goes even further. a crook wouldn't even need to be in your car to gain control of it. the most vulnerable components, wireless technologies like the telematic systems like onstar and car-net.