"We are a long way from securing the non-autonomous vehicles, let alone the autonomous ones. The extra computers, sensors, and improved internet connectivity required to make a car drive itself increase the possible weak points," said Stefan Savage from University of California, San Diego.
"The attack surface for these things is even worse," said Savage.
He said it is possible to take control of conventional vehicles in various ways, for example by dialling into a car's built-in cellular connection, or by giving a driver a music CD programmed with a 'song of death' that makes the car connect to an attacker's computer.
Isolating important parts such as the brakes is not possible as everything must be connected to enable many functions people expect of cars, as well as to allow repairs and software upgrades, Savage said.
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More computers, sensors, and other components must be added to the tangle already inside our cars so that the vehicle is able to understand its environment and drive itself even part of the time.
"It will also magnify a problem that already exists - carmakers do not know exactly what software is inside the vehicles they sell," said Savage.
This is due to the fact that cars are built using components sourced at the lowest possible cost from third-party suppliers.
Those suppliers carefully guard the details of the software inside things like the brake-control system or central locking components.