http://www.autosec.org/pubs/cars-oakland2010.pdf

Short excerpt: Even at speeds of up to 40 MPH on the runway, the attack packets had their intended effect, whether it was honking the horn, killing the engine, preventing the car from restarting, or blasting the heat. Most dramatic were the effects of Device Control packets to the Electronic Brake Control Module (EBCM) — the full effect of which we had previously not been able to observe. In particular, we were able to release the brakes and actually prevent our driver from braking; no amount of pressure on the brake pedal was able to activate the brakes. Even though we expected this effect, reversed it quickly, and had a safety mechanism in place, it was still a frightening experience for our driver. With another packet, we were able to instantaneously lock the brakes unevenly; this could have been dangerous at higher speeds.