Ukrainian authorities have shut down Demonoid.com, one of the largest websites used to share movie, TV, music and other files with BitTorrent peer-to-peer technology.

Investigators raided ColoCall, the data centre in Ukraine that hosts Demonoid's servers, last week, sealing the site's servers and copying information off them, reported TorrentFreak, a blog dedicated to covering news and information about file sharing, copyright issues and the BitTorrent protocol.

TorrentFreak was started in 2005 by a Dutch blogger and has about 150,000 regular users who subscribe to its RSS feed, according to the site. It also posts file-sharing-related updates on Twitter, where it has about 30,000 followers.

The raid came a few days after a large denial-of-service attack overloaded Demonoid servers and crippled the site.

Demonoid is what is known as a torrent tracker, meaning it facilitates communication between users uploading and downloading torrent files with the help of free client software such as Vuze, µTorrent or BitTorrent.

The torrent system of sharing files breaks files up into fragments, which are shared simultaneously and in both directions among a number of peers, who then can continue to share the file once they have a complete copy of it.

Trackers have servers that actively co-ordinate these file transfers, which makes them differ from torrent index sites, or indexers, which simply compile links to trackers and act as a type of search engine for torrent files.

Some BitTorrent sites, including Demonoid, act as both trackers and indexers.

Demonoid among most popular torrent sites

Hundreds of torrent websites exsist, but Demonoid was one of the most frequented. The web metrics site Alexa.com ranked it among the top 600 websites in the world in terms of traffic and the top 300 in the U.S.

If past shutdowns of similar sites, including the popular Pirate Bay, are any indication, the Demonoid closure is unlikely to significantly curb torrent file sharing as users switch to other trackers or wait for Demonoid to emerge in a new incarnation or be replaced by new sites.

TorrentFreak reported that Demonoid had tried to get around violating Ukrainian copyright law by blocking domestic IP addresses from accessing it. But that was apparently not enough to keep the authorities away.

One of Demonoid's administrators was arrested in Mexico last fall, and it was that arrest that led Interpol to contact Ukrainian authorities and request that they shut down the site's servers in Ukraine.

TorrentFreak cited reports in the newspaper Kommersant-Ukraine that speculated that the raid might also have been an attempt to show U.S. authorities that Ukraine is getting tough on copyright infringement.

The paper also reported that the ColoCall data centre had repeatedly warned Demonoid before the recent raid that it had been contacted by law enforcement agencies about Demonoid's alleged copyright infringement and that if the interest from authorities continued, ColoCall would break its contract with Demonoid.

The tracker did not respond to the warnings so ColoCall agreed to disconnect its servers when anti-cybercrime agents arrived at its offices to inspect the Demonoid servers, Kommersant-Ukraine reported.

'Notorious market' for copyrighted material

Demonoid is one of several torrent tracker and index sites flagged by U.S. authorities as a "notorious market" in which pirated goods are reportedly available.

A U.S. government document listing notorious markets says that while torrent trackers and indices can be used for lawful purposes, they also facilitate the dissemination of copyrighted content.

Megaupload founder Kim Dotcom talks to members of the media as he leaves the High Court in Auckland, New Zealand, on Feb. 29, 2012. Dotcom faces possible extradition to the U.S. over allegations of copyright infringement. (Simon Watts/Reuters)

The Demonoid raid is only the latest of several crackdowns on file sharing. In January of this year, U.S. and New Zealand authorities shut down the popular website Megaupload, which allowed users to store and share files on servers that can be accessed remotely. It also appears on the U.S. notorious markets list.

Megauplaod owner Kim Dotcom (as he is officially known) and six of his partners were arrested in New Zealand at the request of U.S. authorities. They allege the site's operators were profiting from the theft of copyrighted content through user fees and advertising, and want them extradited to the U.S. to face charges of copyright infringement, racketeering, money laundering and other offences.

Law enforcement officers seized millions of dollars in assets from the operators of the site, including luxury cars, jewelry and jet skis, although a New Zealand judge later ruled that the seizure was unlawful, and police admitted they made procedural errors when carrying out the search warrant.

The U.S. government's case against Megaupload has been fraught with controversy and missteps. A New Zealand judge hearing the extradition request against Dotcom was forced to step down after he referred to the U.S. Justice Department as the "enemy" in a talk on copyright law.

The extradition hearing has since been postponed to March 2013.

Another judge overseeing the matter in the U.S. recently questioned whether the case will ever make it to trial in the U.S. since the company had not been officially served with papers in the U.S. formally charging it with the alleged offences.