Can you hijack a drive by wire car remotely?
I am convinced that any security system invented by humans can be defeated by humans. There is already a virus out that can establish itself on any computer, connected to the internet or not, inerfere with the computer in the background and report home occasionally:
https://public.gdatasoftware.com/Web/Content/INT/Blog/2014/02_2014/documents/GData_Uroburos_RedPaper_EN_v1.pdf