Since Rodrigo Duterte was elected president of the Philippines last June, he has waged a brutal crackdown on drug dealers and addicts. Nearly 4,000 people have been killed by government forces, and Duterte has invoked the Holocaust to describe the scope of his ambition. “Hitler massacred three million Jews,” he declared in September. “Now there is three million drug addicts. There are. I’d be happy to slaughter them.”

Duterte’s authoritarian rhetoric has elicited sharp condemnations from human rights advocates and foreign leaders. But there’s another front in his war on drugs that has escaped international attention. Last fall, as I reported on the violence in the Philippines, I picked up an ardent critic on social media. Her name was Madelyn, and she was young and attractive, with long hair and deep, brown eyes. When I posted about Duterte’s war on drugs, Madelyn responded with derision. “Maybe u are anti-Duterte TROLL,” she tweeted. “A foreigner who knows NOTHING bout my country.” She seemed to devote her waking hours to spreading her love of Duterte and assailing anyone who questioned him, posting dozens of times a day. “My President and I am proud of him,” one tweet read. “Get lost critics!”

Madelyn, it appears, is part of a vast and effective “keyboard army” that Duterte and his backers have mobilized to silence dissenters and create the illusion that he enjoys widespread public support. Each day, hundreds of thousands of supporters—both paid and unpaid—take to social media to proselytize Duterte’s deadly gospel. They rotate through topics like corruption, drug abuse, and U.S. interference, and post links to hastily cobbled-together, hyper-partisan web sites at all hours of the day and night. Though social media is designed to make each user appear to be a unique individual whose views are her own, Madelyn and her cohort stick exclusively to the Duterte talking points, without any of the cat GIFs, funny asides, jokes with friends, or other elements that populate most people’s feeds.

When Facebook and Twitter were founded a decade ago, they heralded a new era in which the voices of ordinary citizens could be heard alongside—or even above—those of establishment insiders. From the Arab Spring and Occupy Wall Street to Black Lives Matter and recent demonstrations against Vladimir Putin, activists have used social media to attract followers and broadcast their messages free from official oversight. But increasingly, authoritarian regimes like Duterte’s are deploying social media to disseminate official propaganda, crack down on dissent, and maintain their grip on power. What began as a tool of freedom and democracy is being turned into a weapon of repression.

“For authoritarian states, social media censorship will increasingly be seen as an essential aspect of the security apparatus,” says Eric Jensen, a sociologist at the University of Warwick in Coventry, England, who specializes in online public engagement. “There has been a pattern of civil society embracing opportunities for more open communication, such as social media—followed inexorably by a gradual colonization of those communication channels by corporations and government.”