The Pirate Bay site says it plans to be up again shortly

Police said the site was taken offline after it was overloaded by net data.

The attack came a day after the police raided several locations linked to a website accused of directing users to pirated films, music and software.

ThePirateBay.org had described itself as the largest search index for BitTorrent, a system used for sharing large files over the internet.

The entertainment industry welcomed the action against a site it argued was a major source of music and film piracy.

Raids and arrests

Swedish police are investigating the so-called denial of service attack against the website of the national police.

Such attacks are designed to overload a server by bombarding it with data.

It is not clear whether the attack is linked to the police action against The Pirate Bay.

On Wednesday, officers raided 10 locations across the country, confiscating the computers and detaining three men suspected of violating copyright laws.

The three have since been released, but a spokesman said they could still face charges.

Legal questions

The people behind The Pirate Bay argued they were not breaking the law.

They maintain that the site's function was to direct users towards the files that they search for and manage the uploads and downloads. The website itself did not hold any copyright files.

The legality of the website has not been tested in Swedish courts.

The site has been offline since Wednesday, with a statement on its homepage saying that it planned to be up and running again within a few days.

The Pirate Bay became a dominant player in tracking BitTorrent files when another search index, SuprNova.org, met its demise in late 2004.

SuprNova.org, shut down after a relentless campaign by the entertainment industry to close its operations.