I read similar article a while back where they went even further: They were able to disable breaks by messing with ABS control unit and were able to increase speed by remotely controlling throttle... also locking car doors remotely, operating washer/wipers,... you name it. I tried to look for the article (it was in pdf format) but couldn't find it right at the moment.

EDIT: After reading further in the article they mention they experimented with Ford Focus in the past where they disabled the brakes. This sounds very familiar to the article I read before, so must be the same guys?