Four people have been arrested in connection with illegally distributing movies, music and software online. At least eight web sites have been taken down by the FBI, working in conjunction with investigators from 10 other countries including the UK, the US Department of Justice (DOJ) announced yesterday.

The crackdown on piracy distribution sites, known colloquially as warez sites, was a result of 70 searches conducted in the US and another 20 in other countries on Wednesday. Law enforcement authorities identified more than 120 members of what the DOJ called the "organised online piracy underground," DOJ officials said during a press conference. In the warez community, highly organised groups work together to distribute copyrighted materials, often competing with each other to be the fastest to post a free version of a movie or video game.

The DOJ didn't have immediate information on the four people arrested. Action could be taken against further suspects, officials said.

Searches happened in 10 countries in addition to the US: UK, Canada, Israel, France, Belgium, Denmark, the Netherlands, Germany, Portugal and Australia.

The crackdown, called Operation Site Down, resulted in the confiscation of several computers and servers, causing at least eight warez sites to be shut down, said US Attorney General Alberto Gonzales. During Wednesday's action, more than $50m (approx £28m) worth of pirated works were seized by law enforcement, he said.

The DOJ will continue its "aggressive efforts to dismantle international criminal organisations that use sophisticated methods to steal staggering amounts of intellectual property," Gonzales said.

The operation targeted 22 warez groups, including Myth, TDA, HellBound, Corrupt, Gamerz, NOX and Goodfellaz, the DOJ said. The DOJ accused these groups of pirating software such as Autodesk's Autocad 2006 and Adobe's Photoshop and movies such as Mr. and Mrs. Smith and Star Wars Episode III: Revenge of the Sith.

In some cases, the pirated works end up traded through peer-to-peer software, and in other cases, copies are sold to groups that burn CDs and DVDs and sell them on the street, said Michael DuBose, deputy chief of the DOJ's Computer Crime and Intellectual Property Section.

"The theft of this property strikes at the heart of America's economy," said Louis Reigel, assistant director of the FBI Cyber Division. "This theft deprives many Americans and other workers around the globe of their right to be paid for their labour and enjoy the value of their hard work."