It’s no secret that neo-Nazis freely post anonymously all over the internet, every single day. But a recent leak shows that white nationalists online can’t always protect their identities.

The metadata of a now-defunct neo-Nazi message board that is considered the birthplace of several militant organizations—among them the U.S.-based terror group Atomwaffen Division—was dumped onto the internet by what appears to be anti-fascist activists.

The site, IronMarch, is widely associated with the rise of the new wave of white supremacist accelerationst groups advocating for armed insurgency against society. The site ran from 2011 to 2017 and garnered more than 150,000 posts while active. The dump of its inner workings includes the login names of its former members and their associated emails and IP addresses.

Although Motherboard could not verify all the contents of the dump, early record searches match names and details of white nationalist militants tracked by Motherboard over the course of a two-year investigation into neo-Nazi terrorism. The dump also matched internal IronMarch data that Motherboard already accessed.

The identity of whoever originally obtained the data isn’t known, but the dump was uploaded to the Internet Archive by a user named “antifa-data” on November 6.

According to a README file posted with the dump, the data came from a user on an active neo-Nazi forum that succeeded IronMarch, who posted a cache they described as comprising “176 Gigabytes worth of videos, images, and literature all straight from ironmarch.” The original download link for the cache is currently dead.

“Iron March has hosted some of the most dangerous right-wing extremists and featured some of the most extreme far-right content on the surface web in recent years,” said Ryan Scrivens, an assistant professor in the School of Criminal Justice at Michigan State University who studies the far-right.

Often, white nationalists use the same nicknames across several platforms to maintain their personas when sites are shut down for terms of service violations. A dump of this magnitude will aid authorities, academics, and journalists in tracking the identities of anonymous posters and outing real world neo-Nazis from their online hideaways.