When the threatening letters started to arrive, Albert Ponce stopped letting his daughter touch the mail.

Ponce, a political science professor at Diablo Valley College in the San Francisco Bay Area, and his wife didn’t know how to explain to their 9-year-old that her father was receiving death threats. “Only Mom and Dad can touch the mail” became a new house rule.

Each night after putting his daughter to bed, Ponce would peek through the windows of his home in Martinez, California, to check for strange cars or people outside, “precautionary measures,” he said, after an internet troll army had targeted him.

It started just before Christmas last year. Ponce logged in to his college email account expecting the usual: work messages, a few season’s greetings from family and colleagues, maybe some spam. Instead, he found an inbox full of vitriol….