That will be the most common failure mode for computer-driven cars: how easy they are to bring to a stop. (And, yes, that's probably criminal behavior.)
A computer-driven car, though, wouldn't (shouldn't) just immediately slam on the brakes because of that signal. It would tighten seat belts and start slowing down, but it also would want to avoid getting rammed by the car behind it. It can make very accurate estimates about its stopping distance and use all of it.
Until some asshat implements a button that sends this message for "lulz", though that would probably constitute a crime under existing law.