I am always amazed by people thinking that cars haven't been hackable until recently.
People have been hacking the "computers" in Cars since at least the 1970's for ill or good intent. While the computers in a 1972 VM 411 was basically a block of circuits dipped in epoxy.. if you grounded out certain circuits it would change the performance. By the 1980's people were hacking later systems to get around smog controls or change the various speed controls so that you could get different performance. Supposedly in the same logic paths you could also cause the power brakes in certain cars to fail after the car went over X mph depending on what resistor you ran between two terminal points. [The original hack was to turn on the horn and lights when that happened but someone saw that the circuit controlling the breaks was open also.]
While that was physical hacking.. there were chipset hacks once 8 bit controllers got cheap enough for them to be put in.
In all that time, security wasn't considered an issue because well "Who would do that?" and "Well now we have to replace the parts on the next 8 model years if we do that."