LUXEMBOURG:  Internet service providers cannot be forced to install filters aimed at preventing people from illegally downloading files such as music, the EU's top court ruled on Thursday.

The decision by the European Union Court of Justice deals a blow to backers of web filters, including artists and the enterainment industry, who are fighting to protect their work from circulating freely on the Internet.

The judges ruled that web a national court cannot impose an injunction ordering an Internet provider to install a filtering system for all electronic communications, saying it would infringe on customers' fundamental rights.

The case arose from a dispute in Belgium pitting web provider Scarlet Extended SA and SABAM, a Belgian management company responsible for authorizing the use of music of authors, composers and editors.

SABAM complained in 2004 that Scarlet's customers were using peer-to-peer networks, which allow people to share files online, to download works from its catalogue without authorization and without paying royalties.

A Belgian court then ordered Scarlet to make it impossible for its customers to send or receive any electronic files containing SABAM music.

But the EU court ruled that such filters require the monitoring of all electronic communications, which is incompatible with the Union's E-Commerce rules.

An injunction would "result in a serious infringement of Scarlet's freedom to conduct its business as it would require Scarlet to install a complicated, costly, permanent computer system at its own expense," the court said.

"The filtering system would also be liable to infringe the fundamental rights of its customers, namely their right to protection of their personal data and their right to receive or impart information," it added.