In New England in the US, a judge has thrown out an attempt to uncover the names of four students accused of seeking and sharing pirated pop CDs.
The Recording Industry Association of America was trying to identify the students as part of its ongoing program against the web's file-swapping networks.
So far the RIAA has launched legal action against 2,000 people and court proceedings are due to start later this month.
But these plans suffered a small setback last week when a US District judge blocked an attempt by the RIAA to find out the names of students at Boston College and the Massachusetts Institute of Technology it accuses of prolific file-sharing.
The RIAA is seeking the names of three students from Boston College and one from MIT.
But Judge Joseph L Tauro said because the subpoenas were issued in Washington, DC they cannot be served in Massachusetts.
The RIAA called the setback a "minor procedural issue".
It said the ruling "does not change an undeniable fact - when individuals distribute music illegally online, they are not anonymous and service providers must reveal who they are".
The RIAA is pursuing people who swap pop via peer-to-peer networks such as Kazaa, because it claims that such sharing is driving a decline in music sales.
But critics say there are other reasons, such as rampant large-scale CD piracy, that can better account for the decline in music sales.
US net service firms are also resisting RIAA attempts to force them to reveal the names of subscribers who are using file-sharing systems.
About 100 US net providers have written to the RIAA questioning the drive to identify file-swappers and saying they are being forced to become a de-facto police force for the net.
The net firms fear that the hidden agenda of the RIAA is to make them legally responsible for the online conduct of their customers.