Miller couldn’t talk about any of the specifics of his research at Uber; he says he moved to Didi in part because the company has allowed him to speak more openly about car hacking. But he warns that before self-driving taxis can become a reality, the vehicles’ architects will need to consider everything from the vast array of automation in driverless cars that can be remotely hijacked, to the possibility that passengers themselves could use their physical access to sabotage an unmanned vehicle.

“Autonomous vehicles are at the apex of all the terrible things that can go wrong,” says Miller, who spent years on the NSA’s Tailored Access Operations team of elite hackers before stints at Twitter and Uber. “Cars are already insecure, and you’re adding a bunch of sensors and computers that are controlling them…If a bad guy gets control of that, it’s going to be even worse.”