European telecoms and Internet companies are not obliged to reveal the identity of clients who may have illegally-downloaded music recordings, an advisor to the European Union's Court of Justice said Wednesday.

The Advocate General of the Luxembourg-based court, the EU's highest, was ruling on a case involving Spanish telecoms giant Telefonica, which also runs a broadband Internet service.

The case was brought by a Spanish music association Promusicae after Telefonica refused to hand over the names and addresses of its Internet clients suspected of illegally-swapping copyrighted material through peer-to-peer file-sharing program KaZaA.

Telefonica had refused Promusicae's request on the grounds that the law required it to disclose such information for the purpose of criminal prosecutions but not for civil lawsuits.

Advocate General Juliane Kokott said that it is compatible with EU law for European countries to exclude communication of personal data in the context of a civil, as distinct from criminal, action.

The full court will decide definitively on the case in four to six months' time. It backs the Advocate General on average in four out of five cases.