When Wired hacked a Jeep back in July it left no question that today's autos are vulnerable to malicious attacks:

Though I hadn’t touched the dashboard, the vents in the Jeep Cherokee started blasting cold air at the maximum setting...Next the radio switched to the local hip hop station and began blaring Skee-lo at full volume. I spun the control knob and hit the power button, to no avail. Then the windshield wipers turned on, and wiper fluid blurred the glass.

As I tried to cope with all this, a picture of the two hackers performing these stunts appeared on the car’s digital display...

Upon seeing proof that existing vehicles were already at risk, and knowing that up to 75% of vehicles will be wirelessly connected to some network within five years, the software security industry quickly brought defensive measures to market.

But there's plenty auto dealers or auto repair shops can do to help customers protect themselves. Arxan Technologies provides an overview: