A 19-year-old IT and security enthusiast has managed to gain access to a number of Tesla cars in different countries following a vulnerability in third-party software or hardware that they installed. The access included key control features like "disabling Sentry Mode, opening the doors/windows and even starting Keyless Driving," in addition to honking the horn or taking over the car stereo while driving.
https://www.notebookcheck.net/25-Tesla-cars-in-13-countries-hacked-as-a-security-warning-by-a-19-year-old-enthusiast.592607.0.html