The Kazaa file-sharing network will soon change its core software in an attempt to cut music piracy.
Kazaa has until 5 December to impose the filtering system
An Australian court has told Kazaa's owners to impose a filtering system so searches for 3,000 keywords do not let users find copyrighted material.
Kazaa is making the changes to win a chance to have an appeal heard on a copyright case it lost in September.
It is unclear whether the keyword list will limit piracy as many file-swappers have now stopped using Kazaa.
The order by the court is the outcome of the copyright infringement case that Kazaa lost earlier this year.
That case was brought in Australia by more than 30 music labels and ended with Kazaa being found guilty of encouraging users to infringe copyright.
As part of the ruling the federal judge gave Kazaa owners Sharman Networks two months to change its technology to stop people finding and sharing pirated music. That deadline expires on 5 December.
Sharman has won an extension to this deadline by agreeing to put in place the keyword filtering system. The appeal will now be heard in February 2006.
Initially the record labels, represented by the International Federation of the Phonographic Industry, wanted Kazaa to filter 10,000 terms. The court reduced this to a list 3,000 terms long that will be updated every fortnight. Kazaa will have 48 hours to update the lists when they are renewed.
Artists such as Kylie Minogue and Eminem could disappear from Kazaa when the list is imposed.
As another condition Kazaa must make it impossible for users of its updated browsing software to get around the list. It must also make efforts to make as many users as possible upgrade to the restricted version.
For its part Sharman wanted time to put in place another system that used digital signatures of music files to spot and strip out pirated works. In the event the court preferred the keyword list.
It is unlikely that the demands of the court will have a significant impact on the amount of piracy taking place via the Kazaa network as many dedicated file-sharers have moved to other networks to get what they want.
Also few people are likely to download browser software that limits what they can find on peer-to-peer networks.