The four co-founders of website The Pirate Bay have been found guilty of assisting the distribution of illegal content online by a Swedish court today and have been sentenced to a year in jail and a $3.6m (£2.4m) fine.

Charges against the site, which allows web users to access music, movies and TV shows without paying for them and claimed 22 million users during February, were brought by a consortium of media, film and music companies led by the International Federation of the Phonographic Industry.

A Stockholm court found the four defendants guilty of making 33 specific files accessible for illegal sharing through The Pirate Bay, which means they will have to pay compensation to 17 different music and media companies including Sony BMG, Universal, EMI, Warner, MGM and 20th Century Fox.

All four have pledged to appeal against the decision though the process may take several years.

One of the defendants, Peter Sunde Kolmisoppi, admitted on Twitter that Pirate Bay had lost its case.

"Stay calm – nothing will happen to TPB, us personally or filesharing what so ever. This is just a theatre for the media," he said.

"Really, it's a bit LOL. It used to be only movies, now even verdicts are out before the official release."

Pirate Bay logo

John Kennedy, chairman and chief executive of the International Federation of the Phonographic Industry, said: "We're very pleased at the verdict of what was a very important case for us.

"It would have been very difficult to put on a brave face if we had lost, but this verdict sends a strong educational and deterrent message."

The trial began on 16 February in Stockholm district court, when the four co-founders of The Pirate Bay, Fredrik Neij, Carl Lundström, Gottfrid Svartholm Warg and Kolmisoppi, were put in the dock on charges of assisting copyright infringement.

The Pirate Bay does not itself host audio and video files, but provides links to torrents hosted elsewhere on the internet.

Throughout the trial, the Pirate Bay defendants have played up their image as rebellious outsiders, arriving at court in a slogan-daubed party bus and insisting that their position was to defend a popular technology rather than illegal filesharing.

Prosecutors made a major slip-up on the second day of the trial after failing to convince the judge that illegally copied files had been distributed by the site.

They were forced to drop the charge of "assisting copyright infringement" and focus on the lesser charge of "assisting making available copyrighted content". They had been seeking SKr115m (£9.1m) in compensation for loss of earnings due to the millions of illegal downloads facilitated by the site.

The trial has further polarised the tech community and the music industry with both sides eagerly awaiting the result, which will be regarded as a precedent for future filesharing cases.

Supporters of The Pirate Bay held a street party in Moscow last night, with organisers saying the trial had proved that the companies behind the prosecution were "motivated only by their greed and inertia, want to prevent people sharing music, movies, or anything, on a purely altruistic basis".

The chairman of the Swedish Independent Music Producers Association, Jonas Sjöström, said as the trial concluded that the consortium is "tired and sick of services like The Pirate Bay who have no understanding or respect for the creative community, and instead have their own financial interests at heart".

Meanwhile, Sweden's National Museum of Science and Technology announced yesterday that it had bought a server owned by The Pirate Bay confiscated by police last year. The museum paid SKr2,000 for the server and will display it in its archive of illegally copied material.