Yes, hackers can really take over cars. Here’s a Wired article where it’s done on purpose.

Miller and Valasek’s full arsenal includes functions that at lower speeds fully kill the engine, abruptly engage the brakes, or disable them altogether. The most disturbing maneuver came when they cut the Jeep’s brakes, leaving me frantically pumping the pedal as the 2-ton SUV slid uncontrollably into a ditch. The researchers say they’re working on perfecting their steering control—for now they can only hijack the wheel when the Jeep is in reverse. Their hack enables surveillance too: They can track a targeted Jeep’s GPS coordinates, measure its speed, and even drop pins on a map to trace its route.

All of this is possible only because Chrysler, like practically all carmakers, is doing its best to turn the modern automobile into a smartphone. Uconnect, an Internet-connected computer feature in hundreds of thousands of Fiat Chrysler cars, SUVs, and trucks, controls the vehicle’s entertainment and navigation, enables phone calls, and even offers a Wi-Fi hot spot. And thanks to one vulnerable element, which Miller and Valasek won’t identify until their Black Hat talk, Uconnect’s cellular connection also lets anyone who knows the car’s IP address gain access from anywhere in the country. “From an attacker’s perspective, it’s a super nice vulnerability,” Miller says.

From that entry point, Miller and Valasek’s attack pivots to an adjacent chip in the car’s head unit—the hardware for its entertainment system—silently rewriting the chip’s firmware to plant their code. That rewritten firmware is capable of sending commands through the car’s internal computer network, known as a CAN bus, to its physical components like the engine and wheels. Miller and Valasek say the attack on the entertainment system seems to work on any Chrysler vehicle with Uconnect from late 2013, all of 2014, and early 2015. They’ve only tested their full set of physical hacks, including ones targeting transmission and braking systems, on a Jeep Cherokee, though they believe that most of their attacks could be tweaked to work on any Chrysler vehicle with the vulnerable Uconnect head unit. They have yet to try remotely hacking into other makes and models of cars.