KickassTorrents (also known as Kickass Torrents or just KAT) appears to be down. We have had some luck getting it to load, trying both http://kat.cr and https://kat.cr, but, in most cases, the most popular torrent site in the world simply doesn’t work.

The outage comes soon after the arrest of 30-year-old Artem Vaulin, the alleged founder of KAT. The U.S. will seek to extradite the Ukrainian, who was arrested in Poland and has been 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.

The criminal complaint filed in U.S. District Court in Chicago notes that KAT receives more than 50 million unique monthly visitors and is estimated to be the 69th most frequently visited website on the internet. The complaint also states that KAT operates in approximately 28 languages, has a net worth of more than $54 million, and generates an estimated $12.5 million to $22.3 million in annual advertising revenue.

“Vaulin is charged with running today’s most visited illegal file-sharing website, responsible for unlawfully distributing well over $1 billion of copyrighted materials,” Assistant Attorney General Caldwell said in a statement. “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.”

Torrent sites like KAT and The Pirate Bay do not host pirated content themselves, but instead provide links to torrent files that allow users to then download both legally and illegally obtained software, games, music, TV shows, movies, and so on. Torrent files contain the instructions for how to download the content from other users, and BitTorrent clients follow them.

We have not confirmed that KAT is experiencing technical difficulties because of Vaulin’s arrest, but federal authorities in Chicago say they have “seized domain names associated with the website” so it’s unlikely to be a simple coincidence. The domains in question are kickasstorrents.com, kat.ph, kickass.to, kastatic.com, kickass.so, thekat.tv, and kat.cr.

Whether the site stays down or not, users will merely shift to other torrent sites, including copycats that are likely to spring up if KAT is down for long enough.