The most popular torrent-sharing website in the world, Kickass Torrents, often called KAT, is offline as of Wednesday, July 20, after the United States government seized seven of its domains, following the arrest of its alleged owner, Atrem Vaulin, in Poland. The U.S. is also seeking his extradition in relation with four counts of alleged criminal activity.

Exact details of Vaulin’s arrest were not available, but it followed a long investigation by Jared Der-Yeghiayan, a special agent with the U.S. Department of Homeland Security, Immigration and Customs Enforcement, Homeland Security Investigations. The investigation also involved agents from the Internal Revenue Service, according to a complaint and affidavit filed in the U.S. District Court in Chicago on July 8.

Agents, posing as advertisers, made undercover deals with KAT that revealed a bank account associated with the website, which has also been seized. According to the complaint, the 30-year-old Vaulin, a Ukrainian, used the name “tirm” as his online identity and a company called Cryptoneat as a front for KAT.

Following his arrest, Vaulin is being charged “with one count of conspiracy to commit criminal copyright infringement, one count of conspiracy to commit money laundering and two counts of criminal copyright infringement,” according to a statement on the U.S. Department of Justice website.

The statement also accuses Vaulin of stealing “more than $1 billion in profits from the U.S. entertainment industry.” The complaint said “KAT receives more than 50 million unique visitors per month and is estimated to be the 69th most frequently visited website on the internet.”

Assistant Attorney General Leslie R. Caldwell commented on Vaulin’s arrest: “In an effort to evade law enforcement, Vaulin allegedly relied on servers located in countries around the world and moved his domains due to repeated seizures and civil lawsuits.  His arrest in Poland, however, demonstrates again that cybercriminals can run, but they cannot hide from justice.”

KAT uses BitTorrent technology for peer-to-peer file sharing, and in November 2014, overtook Pirate Bay as the most visited torrent directory in the world. The site does not host any illegal content itself, but only provides links to files that can download unauthorized copies of content from other users’ computers. It has been embroiled in legal tangles often, changing its domain several times in the last five years.