Lack of inhibition resulting from anonymity online is a phenomenon psychologists call the Gyges affect, after a Greek myth about a shepherd who possessed a ring that could make him invisible.

“Cyber-psychologists often talk about the disinhibition affect. People do and say things online that they wouldn’t do in real life,” said John Suler, a cyber-psychologist at Rider University in New Jersey. In cyberspace, the face-to-face cues people rely on to curb inappropriate behavior is missing.

“People can’t see you. You can’t see them. You can’t see if people are cringing or looking uncomfortable, and so trolls continue to say things they would never say in a room full of people, Suler told ABCNews.com.

But anonymity alone does not breed trolls, said Claire Hardaker, a professor at Lancaster University in England who studies Internet troublemakers. Trolls often have some sort of personal grudge, she said.