I'd guess frequent and devastating. There is potential for both. For frequency, more cars with more problems means more attack surface, and the longer on the ma

I'd guess frequent and devastating. There is potential for both. For frequency, more cars with more problems means more attack surface, and the longer on the market and more widespread they are the more exposure wannabe attackers get to them. For devastation, in-car firewalls between different systems and buses have been proven ineffective, so remote steering is possible. And some cars even provide remote steering as a feature, like automatic parking. So for an attacker, it is possible to create a lot of property damage and even kill people, so there is the huge potential of ransom and general havoc. For a harmless and maybe easy example, just imagine all cars by a popular manufacturer suddenly deciding to engage the automatic unparking, the stopping and locking down and blocking all the parking lots in the process. For a less harmless and hopefully more difficult one, imagine all those cars suddenly steering hard left when over 80km/h.