Parents at three local high schools are being warned about a social media app that allows people to post hurtful messages anonymously.
The app is called Yik Yak.
Users, who must be at least 17 years old, are able to look at a live feed of anonymous posts made by people in their area.
Officials at New Trier, Lake Forest and Whitney Young High Schools sent letters to parents, alerting them that some teens were using the app to bully other students, even including their names in the posts.
The schools have all blocked the app from their online networks.
Officials said students found using the app could face disciplinary action.