[The] fact that a car is not a simple machine of glass and steel but a hackable network of computers, is what [Charlie Miller and Chris Valasek] have spent the last year trying to demonstrate. Miller, a 40-year-old security engineer at Twitter, and Valasek, the 31-year-old director of security intelligence at the Seattle consultancy IOActive, received an $80,000-plus grant last fall from [the] Defense Advanced Research Projects Agency to root out security vulnerabilities in automobiles. The need for scrutiny is growing as cars are increasingly automated and connected to the Internet. Practically every American carmaker now offers a cellular service or Wi-Fi network like General Motors' OnStar, Toyota's Safety Connect and Ford's SYNC. Without better security it's all potentially vulnerable, and automakers are remaining mum or downplaying the issue. As I drove their vehicles for more than an hour, Miller and Valasek showed that they've reverse-engineered enough of the software of the [Ford] Escape and the Toyota Prius (both the 2010 model) to demonstrate a range of nasty surprises: everything from annoyances like uncontrollably blasting the horn to serious hazards like slamming on the Prius' brakes at high speeds. They sent commands from their laptops that killed power steering, spoofed the GPS and made pathological liars out of speedometers and odometers. Finally they directed me out to a country road, where Valasek showed that he could violently jerk the Prius' steering at any speed, threatening to send us into a cornfield or a head-on collision.