Susan Gerbic spent her career photographing babies at a department store in Salinas, California, just 100 miles south of San Francisco. Today, the retired 55-year-old has dedicated her life to something entirely different: Wikipedia.

As a member of the skeptical movement, Gerbic is committed to promoting critical thinking, scientific inquiry, and empirical evidence—particularly when it comes to fringe ideas. In 2010, she started a Wikipedia project to “improve skeptical content” on the crowdsourced encyclopedia, by writing new articles about topics like people who claim to have supernatural abilities and improving existing ones about groups like those who believe the Earth is flat.

Today, the Guerrilla Skepticism on Wikipedia project has more than 120 volunteer editors from around the world, each of whom Gerbic has recruited and trained herself. They’re collectively responsible for some of the site’s most heavily trafficked articles on topics like scientology, UFOs, and vaccines.

Over the past several years, companies like YouTube, Google, and Facebook have turned to Wikipedia to help fight the spread of misinformation and conspiracy theories on their own platforms. While the crowdsourced encyclopedia isn’t totally immune from being manipulated, it’s proven to be a largely reliable resource for accurate information. GSoW often debunks the same harmful conspiracy theories tech platforms struggle to combat, meaning it stands to play an important role in that battle.

GSoW editors have collectively created or completely rewritten more than 630 Wikipedia pages, which together have garnered over 28 million page visits. They’ve worked in multiple languages in addition to English, including Spanish, French, and Arabic. A private group on Facebook called the Secret Cabal functions as a sort of headquarters, where members discuss edits and decide which articles to tackle next.

Their subjects provide a window into the various ways people end up on Wikipedia, and how they find information on the internet more generally. Take Stan Romanek, a UFO enthusiast who says he’s been contacted by aliens. GSoW editors wrote his page years ago and included information casting doubt on his claims, such as an interview Romanek gave in which he admitted to faking some of his evidence. But the page became newly relevant last July when Netflix added a 2013 documentary called Extraordinary: The Stan Romanek Story to its streaming service. Traffic to Romanek’s Wikipedia page spiked that month, reaching nearly 45,000 visitors one day.

The incident wasn’t a fluke; platforms like Netflix have the power to drive traffic to Wikipedia in other circumstances, too. For example, GSoW wrote the page for What the Health, a vegan documentary also released last year that was criticized for its claims about the risks of eating meat and dairy. It now has over 600,000 page views. But Gerbic’s team just as often finds itself fact-checking dubious claims from their family and friends.

My Friend's Fake News

Robin Cantin, 47, a public servant from Montreal who edits in French and English, joined GSoW last year. At the time, people close to him had just been diagnosed with cancer, and well-meaning friends were sending unscientific health information they found online.

“People sent me links to miracle cures on the web, to try carrot juice, to try oxygen therapy,” Cantin says. “Wikipedia gave clear information about those strange things. I saw what [Wikipedia editors do] as a solution to something I was experiencing personally.”

Since joining GSoW, Cantin has worked on pages for miracle cures, but he particularly likes creating pages for scientists and science communicators, especially if they’re from Canada. He created the page for Jennifer Gunter, a Canadian-American gynecologist and author known for challenging health claims made by celebrities. (She’s the doctor who said it’s not a good idea to put Gwyneth Paltrow’s jade eggs in your vagina.)

'I saw what [Wikipedia editors do] as a solution to something I was experiencing personally' Robin Cantin, Guerrilla Skepticism on Wikipedia editor

Rob Palmer, 60, a GSoW editor from New Jersey, says he’s also written articles to refute claims made by friends and family. He overheard his coworkers raving about the health benefits of elastic therapeutic tape—a type of adhesive cotton athletes wear supposedly to treat pain—and decided to look into it. It turns out that scientists have found few real health benefits associated with wearing the tape, so Palmer edited Wikipedia to reflect that. Sticky cotton tape might seem obscure, but as Palmer points out, it was worn by numerous athletes during the Winter Olympics in South Korea earlier this year.