The previous owners of used "smart" cars can still control them via the cars' apps (not just cars!)

https://www.youtube.com/watch?v=4Nv1dmE_yJ8&feature=youtu.be

It's not just that smart cars' Android apps are sloppily designed and thus horribly insecure; they are also deliberately designed with extremely poor security choices: even if you factory-reset a car after it is sold as used, the original owner can still locate it, honk its horn, and unlock its doors. (more")