COPENHAGEN, Denmark -- The Swedish founder of the file-sharing site The Pirate Bay is suspected along with a Dane of hacking into a company handling sensitive information for the Danish police, officials said Thursday.

Denmark's justice minister said hackers accessed "some information" from the Schengen Information System, a large European database on police and judicial co-operation. He didn't give further details.

Police in Denmark announced the investigation Thursday, and a source close to the probe told The Associated Press that one of the suspects is Pirate Bay founder Gottfrid Svartholm Warg, who was arrested in Cambodia last year and repatriated to Sweden where he is in custody, suspected in a similar case. The source spoke on condition of anonymity because he is not allowed to speak to the media on the record.

A 20-year-old Danish suspect was arrested Wednesday. Before being jailed for four weeks in pretrial custody Thursday, the Dane, who was not identified under Danish privacy rules, pleaded not guilty, said his lawyer, Michael Juul Eriksen.

National police chief Jens Henrik Hoejbjerg said the hackers copied some 4 million pieces of data but there was no immediate evidence it had been used.

"This is a very serious hacking attack on Danish police registers," Justice Minister Morten Boedskov said.

In January, police in Sweden told colleagues in Denmark about a Danish IP address they had found during an investigation into hacker attacks against a company handling sensitive information for the Swedish tax authority. Hoejbjerg said copied information in Denmark also included social security numbers and data from a national register on public and private businesses.

Grave cases of hacking are punishable by up to six years in prison under Danish law.

Svartholm Warg, the Swedish founder of The Pirate Bay, was convicted in Sweden of copyright violations in 2009, along with three Pirate Bay colleagues. Sweden issued an international arrest warrant after he failed to show up for an appeals hearing during which his one-year prison sentence was upheld.

He was deported from Cambodia last year at the request of Swedish authorities who suspect him in another case -- the hacking of the Swedish tax authority -- but no charges have been filed.

The Pirate Bay is one of the world's biggest free file-sharing websites, offering millions of users a forum for downloading music, movies and computer games.

It is still running, despite the convictions of Svartholm Warg and three co-defendants, who were ordered to pay 46 million kronor ($6.5 million) in damages to the entertainment industry.