Advances in technology allow prank callers to mask their voice, phone number or IP address, or make their false 911 calls sound more credible.

Author Patrick Tomlinson and his wife, business owner Niki Robinson, have been “swatted” at their home in Milwaukee more than 40 times, often resulting in police pointing guns at their heads. Their tormentors have also called in false bomb threats to venues using their names in three states. Yet law enforcement hasn’t been able to stop the prank calls.

The couple’s terror comes as these incidents appear to be on the rise in the U.S., at least on college campuses. In less than a single week in April, universities including Clemson, Florida, Boston, Harvard, Cornell, Pittsburgh, Rutgers and Oklahoma, as well as Middlebury College, were targeted by swatters.

To combat the growing problem, the FBI has begun taking formal measures to get a comprehensive picture of the problem on a national level.