Social network operators cannot be forced to filter out content such as copyrighted music, the European Union's highest court ruled today.

Such a system would fail to adequately protect the personal data of social networking users, said the EU Court of Justice (ECJ).

"The owner of an online social network cannot be obliged to install a general filtering system, covering all its users, in order to prevent the unlawful use of musical and audio-visual work," it confirmed.

Netlog, which says it has around 95 million users in Europe, was described by the ECJ as a hosting service provider in the ruling.

The court said:

Such preventive monitoring would therefore require active observation of the files stored by users with the owner of the social network. Accordingly, the filtering system would require that owner to carry out general monitoring of the information stored on its servers, something which is prohibited by the E-Commerce Directive. The Court next recalls that, in the context of measures adopted to protect copyright holders, national authorities and courts must strike a fair balance between the protection of copyright and the protection of the fundamental rights of individuals who are affected by such measures.

That decision is another blow for Sabam – a Belgian artists' and authors' rights group that had complained about the practices of social networking outfit Netlog.

The pro-copyright organisation previously won a court order in 2007, forcing Belgian ISP Scarlet Extended to come up with a filtering system that blocked users from illegally downloading copyrighted material.

In November last year the ECJ ruled that Scarlet should not have to filter copyright-infringing traffic from its service because to do so would invade users' privacy.

The Register asked Sabam to comment on this story, but it hadn't got back to us at time of writing.

The ruling is here. ®