With each beep or buzz, a message flashes across the screen: You're ugly. No one likes you. You're a slut. You should kill yourself.
About half of American teens receive similar personal attacks - verbal or visual cyberbullying - on their phones or computers each year. That's up from about zero just a decade ago.
The reverberations trickle onto schoolyards and into classrooms, where distraught students can't focus, avoid interacting, or skip school altogether to avoid embarrassment or threats.