Sitting in front of a computer not long ago, a tenured history professor faced a challenge that billions of us do every day: deciding whether to believe something on the Internet.

On his screen was an article published by a group called the American College of Pediatricians that discussed how to handle bullying in schools. Among the advice it offered: schools shouldn’t highlight particular groups targeted by bullying because doing so might call attention to “temporarily confused adolescents.”

Scanning the site, the professor took note of the “.org” web address and a list of academic-looking citations. The site’s sober design, devoid of flashy, autoplaying videos, lent it credibility, he thought. After five minutes, he had found little reason to doubt the article. “I’m clearly looking at an official site,” he said.