The Web site of Sweden's national police was shut down after a hacker attack that investigators on Friday said could be a retaliation for a crackdown on a popular file-sharing site called The Pirate Bay.

Meanwhile, the government faced allegations that police had acted under pressure from U.S. authorities when they targeted the file-sharing site in raids earlier this week. The police Web site was closed late Thursday after a so-called denial of service attack, in which hackers overload a single network by directing massive traffic to the site, police spokesman Lars Lindahl said. He did not rule out that the attack was linked to the police crackdown on The Pirate Bay on Wednesday.

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