Users of FaceTime, Apple's ultra-popular video calling app, have been subjected to an unusual kind of attack for a while now. Countless people unwanted prank calls by the hundreds, calls which exploit FaceTime's group-calling system to initiate a self-perpetuating circle of spam—and the victims have no way to stop it.

The way that these spammers have been working is by making a group call to a large number of people, and hanging up quickly afterwards. This initiates an endless string of callbacks when those included in the call begin to realize they've missed a call, and redial ...