On March 24, Timothy Wilson, 36, was shot and killed by the FBI as he prepared to attack a hospital in the Kansas City area where patients with the coronavirus were being treated.

The FBI had previously identified Wilson as a “potentially violent extremist” who had considered attacking a mosque, a synagogue, and a school with a large number of black students before settling on the hospital. He died in a shootout when federal officers tried to arrest him. Hours before his death, Wilson had posted anti-Semitic messages on two white supremacist groups on the messaging app Telegram.

As COVID-19 continues to spread around the world, white supremacists are seizing upon it as a new and powerful addition to their arsenal. Their messaging often happens on Telegram, which over the last year has become a staging ground for extremist groups, according to the Anti Defamation League. Telegram channels associated with white supremacy and racism grew by more than 6,000 users over the month of March, according to data shared exclusively with TIME by the Institute for Strategic Dialogue, a London-based think tank that monitors extremism and disinformation. One white supremacist channel specifically focused on messaging related to COVID-19 grew its user base from just 300 users to 2,700 in that month alone — a growth of 800%.

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In openly-accessible Telegram channels with thousands of members, TIME observed users sharing memes and messages — some couched in purported irony — encouraging people with the disease to infect others, specifically ethnic minorities. “We’ve seen a number of cases of people suggesting that they should deliberately spread it, making themselves into a bio weapon,” says Jacob Davey, a senior research manager at the Institute for Strategic Dialogue. “Which really needs to be taken seriously, even if it is presented in the guise of dark humor.” Other messages seen by TIME celebrated the spread of the virus in Israel and Africa; still more complained, using racist language to refer to Mexicans, that COVID-19 would cause a wave of immigration across the U.S. southern border.

“As stated in our Terms of Service, we do not allow posts that feature calls to violence on publicly viewable Telegram channels, bots, or groups,” a Telegram spokesperson told TIME. “We process reports from users and posts that violate this rule are removed.”

While Telegram channels tend to reach relatively few people compared to larger social media platforms like Twitter or Facebook pages, experts say they are equally if not more dangerous as hubs for extremists. Within these extremist communities, “success isn’t measured by creating a mass movement,” says Cassie Miller, a senior research analyst at the Southern Poverty Law Center (SPLC). “Their end goal is to get people to act on these beliefs, and to do so violently.”

Telegram states on its web site that it will not engage in “politically motivated censorship.” It says that while it does remove terrorist content, “we will not block anybody who peacefully expresses alternative opinions.” But analysts argue much of the white supremacist content on Telegram meets the definition of terrorism. “There are still channels that we look at every single day, including those that glorify violence, including those that have videos of the Christchurch shooting, that are encouraging people to violence against specific communities, and sometimes specific people,” says Oren Segal, vice president of the center on extremism at the Anti Defamation League. “And so the fact that we can still find that regularly tells us that not enough is being done.” Telegram told TIME it has recently set up “a new system for verifying channels” to combat misinformation, and that searches for “corona” now always bring up an official channel with reliable information.

High anxieties surrounding traumatic global events often correlate with the rise of new conspiracy theories. But a new factor driving the increase in coronavirus-related extremism, experts say, is that so many people are now spending time online while confined to their homes. “You basically have a captive audience. It’s not surprising that there’s going to be more online activity,” says Segal. “One of the things we’ve seen is a lot of propaganda being created around coronavirus in the hopes of attracting a new audience.”

The Anti Defamation League has also seen coronavirus-related messaging spreading rapidly on Telegram over the last four months. In the early weeks of the virus’ spread, Segal says, the group found many conspiracies linking the virus to Jewish people and the Chinese government, mobilizing established anti-Semitic and anti-Chinese tropes. Only recently, he says, have members of these groups begun to discuss how to weaponize the virus to attack minorities.

One strand of white supremacist thought, visible in Telegram channels, that has seen a rapid uptick as coronavirus spreads is “accelerationism,” a fringe philosophy that calls for adherents to do all they can to hasten societal collapse and bring a white supremacist government to power in the U.S. “This is a group of the most extreme extremists who are actively welcoming chaos and violence,” says the SPLC’s Cassie Miller. “They have welcomed coronavirus, because it means that we might get pushed closer to civilizational collapse, which is their goal because only after that happens can they build their white ethnostate.”

Telegram is the main place on the Internet where accelerationists congregate, Miller says. “It is the friendliest platform to their thinking,” she says. “They haven’t seemed to make any moves to remove this content.”

Telegram is not just used by extremists: it is also popular among activists and journalists because of its privacy credentials. But it has become a hub for white supremacists at the same time that mainstream social media platforms like Twitter, Facebook and YouTube have tried to crack down on hate speech and violent extremism. While those platforms have also been criticized for doing too little to remove harmful content, they have still largely managed to expel their most openly racist users, along with content which calls for real-world violence, according to Davey. On Telegram, by contrast, “the lack of direct enforcement has really made it a safe haven for these groups,” he says.

With the pandemic bringing the dangers of disinformation to the front of the public mind, pressure is building for Telegram to revisit its long-held policy of putting privacy ahead of protecting vulnerable groups. “Telegram needs to get its act together,” says Segal of the Anti-Defamation League. “Anybody who is researching, tracking and trying to mitigate the threat of extremism is spending a lot of time on Telegram right now.”

Please send tips, leads, and stories from the frontlines to virus@time.com.

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Write to Billy Perrigo at billy.perrigo@time.com.