Someone figured out how to remotely take control of Chrysler vehicles with the Uconnect 8.4 systems a while back. So people are out there working on these things. Also, the more popular the car, the more likely someone is working on it.
To FCA’s credit in that case, they listened to the researchers and implemented several fixes very quickly to address the problem. I wouldn’t put it past many manufacturers to do the hands-over-the-ears “la la la” thing when faced with the same situation.
Are you talking about people breaking in and stealing them? While I agree that was a stupid problem, it’s quite a bit different than a remote hacker taking over your brakes while you drive.