The internet is full of bad people. This is not breaking news.

But in the past week, the anti-Semitic corners of social media have received increased attention because of sustained harassment campaigns against journalists and other public figures and a highly visible effort to combat them by Twitter users.

Jonathan Weisman, the deputy Washington editor at The New York Times, created a stir when he said Wednesday he would quit Twitter, where he had almost 35,000 followers. He was fatigued by a month’s worth of anti-Semitic messages and photos sent his way, an experience he wrote about in May.