The U.S. has dealt a major blow to KickassTorrents, one of the world’s most popular illegal files-sharing websites.

On Wednesday, law enforcement in Poland arrested the alleged owner of the site, 30 year-old Artem Vaulin of Ukraine.

He's been charged with criminal copyright infringement, and the U.S. Department of Justice said it was seeking to extradite him to the U.S. The DOJ also seized several domains associated with the service, although the main site appeared to be still running Wednesday afternoon.

KickassTorrents, also known as KAT, has distributed well over $1 billion in copyrighted materials, prosecutors said. Since 2008, the service has run a directory for downloading pirated movies, TV shows, music and more using the BitTorrent protocol.

Fifty million unique users visit the site every month, the department alleges.

Vaulin, who went by the screen name "tirm," is believed to have designed KickassTorrents' original website and overseen its operations.

"During the latter part of the conspiracy, Vaulin allegedly operated KAT under the auspices of a Ukrainian-based front company called Cryptoneat," the DOJ added.

To evade law enforcement, Vaulin allegedly moved his domains to servers across the world, following repeated seizures and lawsuits. Courts in the U.K., Italy and Malaysia have blocked the site.

Vaulin was also charged with money laundering. The file-sharing site generated up to $22.3 million in annual advertising revenue, the U.S. alleged.

It's unclear what the DOJ will do with the domains it has seized, which include kickasstorrents.com, kastatic.com, thekat.tv, kat.cr, kickass.cr, kickass.to and kat.ph.

Law enforcement agencies have also targeted The Pirate Bay, another illegal file-sharing site. In Dec. 2014, police raided its servers, though the site was only temporarily shut down.