CNET: Tesla hackers explain how they did it at DEF CON 23. http://google.com/newsstand/s/CBIwtYXawyI

Interesting, but here's the spoiler: the hack isn't likely to be useful to anyone. Sounds like Tesla have done a good job.

Impressive stuff from Tesla

So, if you spot someone with a laptop frantically running behind your Tesla trying not to run out of cable, don't slow down: If you do slow to under 5mph he could gently apply your breaks remotely.  Other than that, all good!