The rumors spread like wildfire: Muslims were secretly lacing a Sri Lankan village’s food with sterilization drugs. Soon, a video circulated that appeared to show a Muslim shopkeeper admitting to drugging his customers—he had misunderstood the question that was angrily put to him. Then over a several-day span, dozens of mosques and Muslim-owned shops and homes were burned down across multiple towns.

The rumors were spread via Facebook, whose newsfeed algorithm prioritized high-engagement content, especially videos. “Designed to maximize user time on site,” said a New York Times article. The algorithm “promotes whatever wins the most attention. Studies have found that posts that tap into negative, primal emotions like anger or fear produce the highest engagement.”

Similar cases of mob violence have taken place in India, Myanmar, Mexico, and elsewhere, with misinformation spread mainly through Facebook and the messaging tool WhatsApp.

This happened despite Facebook’s decision in January 2018 to tweak its algorithm, to prevent this kind of deception that leads to violence. But these changes may actually have made the problem worse. An article in the Columbia Journalism Review explained why: “misinformation is almost always more interesting than the truth.”