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The FBI recently took down the what it called "the largest remaining known child pornography hidden service in the world," catching at least 1,500 pedophiles in the process. They did it by temporarily running the site on their own servers and hacking into over a thousand computers that connected to it through the Dark Web.

According to a report from Vice's Motherboard, the child pornography site, which -- horrifyingly -- was called "Playpen," had nearly 215,000 members and featured "some of the most extreme child abuse imagery one could imagine," along with "advice on how sexual abusers could avoid detection online."

Motherboard reports that the FBI took "unprecedented" measures to hack the site: First, in February of 2015, they confiscated the computer server that was running Playpen during a raid. But instead of shutting it down immediately, the FBI then secretly ran the site on their own servers from February 20 to March 4 of 2015, deploying a hacking technique as a Network Investigative Technique, or NIT, which infected all targets who visited the site during that time to capture their IP addresses.

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"Basically, if you visited the homepage and started to sign up for a membership, or started to log in, the warrant authorized deployment of the NIT," Colin Fieman, a federal public defender for several of the people accused told Motherboard, adding that he expected at least 1,500 court cases to come out of the investigation.

Although no one's upset that the site was taken down or that pedophiles are coming to justice, some people are concerned about the FBI's broad application of these hacking techniques.

Fieman, for example, described the operation as an "extraordinary expansion of government surveillance and its use of illegal search methods on a massive scale."

Christopher Soghoian, principal technologist at the American Civil Liberties Union (ACLU), told Motherboard, "This kind of operation is simply unprecedented. We're not talking about searching one or two computers...we're talking about the government hacking thousands of computers, pursuant to a single warrant."

“Although the application for the NIT in this case isn't public, applications for NITs in other cases are,” Soghoian continued. “Time and time again, we have seen the Department of Justice is very vague in the application they're filing. They don't make it clear to judges what they're actually seeking to do. They don't talk about exploiting browser flaws, they don't use the word 'hack.'"

Soghoian also suggested that this kind of hacking by law enforcement is something we should all take very seriously. "This is a scary new frontier of surveillance, and we should not be heading in this direction without public debate, and without Congress carefully evaluating whether these kind of techniques should be used by law enforcement," he told Motherboard.