The Pirate Bay website does not host content but offers a search engine and catalogue of links to access content stored elsewhere on the internet, including music, video and games files. Most of the content is provided in breach of copyright law.
The links download BitTorrent files, small files that are used to download the music and movie files quickly from several other users at once.
Four men face a trial in Sweden as prosecutors seek to shut down the service. The four men – Frederik Neij, Gottfrid Svartholm Warg, Peter Sunde Kolmsioppi and Carl Lundstorm – have tried to attract as much attention as possible to the trial.
Prosecutors have had to drop the more serious charge of 'assisting copyright infringement' and try to prosecute the men on the charge of 'assisting making available copyright material', according to news reports from the trial today.
The lawyer for several music companies involved in the case said that the change was "largely a technical issue", according to the BBC. Torrentfreak reported defence lawyer Per E Samuelson as saying that the decision was "a sensation. It is very rare to win half the target in just one and a half days".
Pirate Bay claims that it does not break the law because it does not host or disseminate copyright-infringing content, it only links to that content.
Technology law specialist Struan Robertson of Pinsent Masons, the law firm behind OUT-LAW.COM, said that the change in charge could make the prosecutors' job more difficult.
"If the only charge is 'assisting making available copyrighted content', it may be more difficult to prove than contributory infringement, which appeared to be the main original charge," he said. "The challenge will be in convincing a court that Pirate Bay, as an intermediary rather than a host, is itself making the content available."
Robertson said that there is a similar offence in the UK, and that the result in Sweden could be influential here.
"We also have a provision in UK legislation that bans knowingly 'making available' copyrighted content without authority, though only where that is done 'by electronic transmission'. It has never been tested in court against a service like Pirate Bay's, so the ruling in Stockholm could be influential for any similar cases that go to trial in the UK," he said.
"What we may find is that the Stockholm court simply concludes that the Pirate Bay looks illegal and sounds illegal – and therefore takes a more liberal interpretation of the law in order to establish that an offence has been committed," said Robertson.
Reports from the court case have said that the prosecutor was not able to prove that the files being shared used Pirate Bay's tracker, and that that was the reason the more serious charge was dropped.
Robertson said that the case the prosecutor is left with is weaker than it was, and that the contributory infringement charge would be the correct one in a case where the evidence backed it up.
"There would be a reasonable case for contributory copyright infringement if it can be established that a site links to infringing content and that it has few non-infringing uses," he said. "That has happened already in the US – it was an argument that helped to defeat Grokster, the P2P service, in the US Supreme Court in 2005."
"Unlike Sweden and the US, we don't have a law against contributory copyright infringement in the UK," said Robertson. "The charge here would either be that the site was 'making available the works by electronic transmission' or that it was 'authorising' the infringement."
Prosecutors would have to convince a court that linking amounts to electronic transmission, he said. The alternative argument is also uncertain.
"The 'authorising infringement' argument failed in the House of Lords in 1988 in a dispute over the legality of twin cassette decks, because the technology had substantial non-infringing uses as well as infringing ones," said Robertson, "but it succeeded more recently in Australia, in a case against the owner of P2P network Kazaa."
In that case, the court ruled that Sharman Networks had failed to take steps to reduce infringement and even encouraged it.
