>> reporter: will haskill says comments like this appeared on an app last month and spread around his high school like a virus. trying to raise awareness, he wrote about the new bullying tactic. >> students who were targeted were blind sided. many teachers and administrators downloaded it. it really did take over the high school. >> i tried not to look, but i was fascinated that students were, like i said, capable of making these terrible comments. >> reporter: now that school is on lockdown. electronically. responding to complaints, the creators of the app set up geo fencing using coordinates to prevent the app from being used on school grounds, protecting 85% of all middle and high schools, an unprecedented step. >> we made our app 17 plus, but we as app developers realized how most parents don't know how to block apps on their children's phones. that's part of the reason we took the measure to disable it on school campuses. >> reporter: paula todd wrote the book "extreme mean." >> sure, it would be a lot easier just to ignore what's going on. but in order to ignore what's going on,