In a blow against the music industry, the European Court of Justice has ruled that EU countries don't have to require internet service providers to reveal subscriber data for use in civil cases.

The Luxembourg court said EU nations may decide on their own whether to require such disclosure, but advised them to seek a balance between disclosing personal information and protecting intellectual property.

Existing EU directives on intellectual property do not require disclosure of personal data to ensure effective protection of copyright, the court said in a news release.

The court's decision means that music and film industry groups may have to find other ways in some countries to identify those suspected of illegally sharing files without the permission of the copyright holder.

It also bolsters prevailing opinions in Europe that an IP (Internet protocol) address - which identifies the computer used by a person - is personal data that should be protected.

The case, initiated in June 2006, arose after Spanish operator Telefónica resisted turning over subscriber data to Promusicae, a nonprofit organisation for music and video publishers in Spain.

Promusicae sought to identify people using the Kazaa peer-to-peer file-sharing program. Promusicae asked Telefónica to name the people who held accounts connected with the IP address of the computer used to share files.

Telefónica contended the data could only be released in the course of a criminal investigation or a national or public security matter.

The IP address of a computer can often be linked to the person who holds an account with an internet service provider, although it won't indicate who was using the computer when the illegal activity happened.

Music industry groups have typically sought to receive damages from those found to be illegally sharing files. Those lawsuits, however, have often been filed against people who hold subscriptions with a provider. In those cases lawyers have argued, mostly unsuccessfully, that the alleged file sharing was perpetrated by people other than those who held the subscriptions.