As cars become more like PCs on wheels, what’s to stop a hacker from taking over yours?

In recent demonstrations, hackers have shown they can slam a car’s brakes at freeway speeds, jerk the steering wheel and even shut down the engine — all from their laptop computers.

Car hacking is not a new field, but its secrets have long been closely guarded. That is about to change, thanks to two well-known computer software hackers who got bored finding bugs in software from Microsoft and Apple.