Digital license plates, already legal to buy in a growing number of states and to drive with nationwide, offer a few perks over their sheet metal predecessors. You can change their display on the fly to frame your plate number with novelty messages, for instance, or to flag that your car has been stolen. Now one security researcher has shown how they can also be hacked to enable a less benign feature: changing a car's license plate number at will to avoid traffic tickets and tolls—or even pin th...