A rash of hoax calls about active shooters on college campuses has spread fear among students around the country as the school year begins at institutions of higher learning.

The calls have prompted schools to issue campus-wide texts to “run, hide, fight.” They've also sent students and teachers running for cover, seeking safety in utility closets or huddling in classrooms. Officers swarmed campuses looking for the threat. In every case, the threat didn’t exist.

The hoax calls and false alarms have hit at least 12 college campuses from Arkansas to Pennsylvania. Security experts say that risk remains, but campus officials must find the right balance in keeping students and teachers on guard for any real threats in the future.