The British music industry has been granted a court order forcing internet service providers (ISPs) to reveal the names of illegal music swappers.
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ISPs have 14 days to hand over names and addresses of 28 alleged uploaders - those who make music available to share with others - to the BPI trade group.
"We will not hesitate to take action against those who infringe our members' rights," said Geoff Taylor of the BPI.
The 28 individuals will be given the chance to settle out of court.
If they do not the BPI (British Phonographic Industry) will seek damages and an injunction to stop them using file-sharing services.
"On the face of it this appears to be a powerful case of copyright infringement," said Mr Justice Blackburne on making the order at the High Court in London.
CD sales have been in decline
Mr Taylor said he was pleased with the decision, adding that the BPI was encouraged by the judge's comments.
"We have been warning for months that unauthorised file-sharing is illegal. These are not people casually downloading the odd track," said BPI chairman Peter Jamieson earlier this month.
"They are uploading music on a massive scale, effectively stealing the livelihoods of thousands of artists and the people who invest in them."
The BPI believes 15% of file-sharers are responsible for 75% of all illegal music downloading.
Music file-sharers have been blamed by the industry for a decline in world-wide CD sales.
US record companies have already issued more than 5,700 lawsuits from alleged file-sharers, with many settling out of court.
There was an outcry when a 12-year-old girl from New York was served with a lawsuit by the US industry, which was eventually settled by her mother.