The key fob sends out a code which the car interprets to unlock the doors. Typically these codes are randomized to prevent hackers from reusing a previous code, but Subaru's implementation is flawed.

"An attacker can 'clone' the key fob, unlock cars and, when increasing the rolling code with a sufficiently high value, effectively render the user's key fob unusable," Wimmenhove wrote.

If you're looking to pick up a new key fob, or repair one, you might wonder how long programming it takes and whether or not you can do it yourself.

A computer engineer found the Subaru key fob's rolling code – the internal system used to securely lock and unlock car doors – was "predictable".

Tom Wimmenhove, a Dutch electronics designer, has discovered a flaw in the key fob system used by several Subaru models, a vulnerability the vendor has not patched and could be abused to hijack cars.