Internet traffic dropped sharply in Sweden last week after a new law cracking down on online copyright violation went into force, experts said.

Based on the European Union's Intellectual Property Rights Enforcement Directive, the new law makes it easier to prosecute file-sharers because it requires Internet Service Providers to disclose the Internet Protocol-addresses of suspected violators to copyright owners.

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Statistics from the Netnod Internet Exchange, an organisation measuring internet traffic, suggest that daily online activity dropped more than 40 per cent after the law took effect last Wednesday.

Henrik Ponten of the Swedish Anti-Piracy Bureau welcomed the plunge in internet traffic as a sign that file-swappers are reducing their activity for fear of getting caught. "There's no other explanation for it," he said.

Some criticised the new law as overzealous and said it puts as risk Sweden's position as a leader in online technologies.

"Half the internet is gone. If this pattern keeps up, it means the extensive broadband network we've built will lose its significance," said Jon Karlung, chief executive of Banhof, a Swedish ISP.

Sweden has one of the highest internet penetration rates in Europe but has also made a name for itself as a hub of illegal file-sharing.

Twelve hours after the law came into force, five Swedish audio book publishers representing 15 authors filed a request to find out details of a server suspected of containing more than 2,000 illegally downloaded works.

In a separate case, four Swedes linked to one of the world's most popular file-sharing sites - The Pirate Bay - are on trial on copyright charges. A verdict is expected this month.