Driverless cars could ignore road signs on the streets since they can be confused by simple vandalism, researchers have found.

While carmakers have been investigating ways to protect autonomous cars against hackers, more conventional attacks could confuse the vehicles into misreading road signs that would appear normal to ordinary drivers.

Placing stickers or posters over part or the whole of a road sign could be used to trick the smart car into ignoring stop signs, even if visually they appear the same to the human drivers.

Researchers at the University of Washington demonstrated how car hackers who had gained access to the visual recognition software within the vehicle could create simple alterations to road signs that would cause the car to misread them.

The researchers said changes that trick learning algorithms, such as those used in driverless cars, can cause them "to misbehave in unexpected and potentially dangerous ways."