In an ongoing investigation into the security of Chrysler vehicles, researchers have found a zero-day exploit that affects about 471,000 vehicles. If you think that sounds bad, that’s because it is. Put in layman’s terms: researchers have found a way hackers can take complete control of the vehicles, even from thousands of miles away.

Innovative car hackers Charlie Miller and Chris Valasek showed Wired the dangerous possibility of the Chrysler exploit. Journalist Andy Greenberg took a Jeep Cherokee out onto the highway, and the two car hackers took control. They used the Jeep’s Uconnect system, which hooks up to a cellular network, to gain control of the car’s entertainment system. From there, they rewrote the firmware to send commands to such parts of the vehicle as the brakes, steering, and transmission.

“This wasn’t the first time hackers have proven they can compromise a car,” says Tom Ajello, Founder/Creative Director, Makeable. “The last one was in the summer of 2013. The scary difference this time is that it now can be done wirelessly. All of this is possible only because Chrysler, like practically all carmakers, is doing its best to turn the modern automobile into a smartphone. Hundreds of thousands if not millions of vehicles now have systems that control the vehicle’s entertainment and navigation, enables phone calls, and even offers a Wi-Fi hotspot. Vulnerable elements related to the cellular connection in things like OnStar, UConnect, etc. also let anyone who knows the car’s IP address gain access—from anywhere. Yikes.”

The two plan to publish a portion of their find online, and will debut it as they give a talk at the Black Hat security conference in Las Vegas next month.

Chrysler has released a patch that can fix the issue, but it needs to be installed either via a USB drive, or by a dealer. In other words, thousands upon thousands of vehicles may remain vulnerable.

The automotive manufacturer isn’t pleased with the researchers, either, and has issued a statement castigating them.

“Under no circumstances does [Fiat Chrysler Automotive] condone or believe it’s appropriate to disclose ‘how-to information’ that would potentially encourage, or help enable hackers to gain unauthorized and unlawful access to vehicle systems,” read the statement.

Although this isn’t the first time hackers have been able to gain access to a vehicle, this latest exploit is pretty serious. In 2013, Miller and Valasek took control of a Ford Escape and a Toyota Prius, disabling brakes, honking the horn, jerking the seat belt, and commandeering the steering wheel.

Back then, however, they had to wire their computers into the vehicles’ onboard diagnostic port to take control. Now, they can do it wirelessly, from thousands of miles away.

“When you lose faith that a car will do what you tell it to do,” said Miller at the time, “it really changes your whole view of how the thing works.”