The world is a dangerous place. If I wanted to do harm to you via your car, two minutes with a pair of side-cutters on your brake lines would do the trick a lot more certainly than some airy fairy attempt to take remote control using your i-phone.
Contrary to the wild imaginings of Hollywood, television producers and crime writers, no driver would fail to discover cut brakes long before their lack became life threatening (Unless of course you start your journey steeply downhill and you don't press the brake pedal at any time before you start off on your journey to infinity and beyond).