A federal judge ruled Friday that the operators of two peer-to-peer online file-sharing companies aren't responsible for illegal music and movie copying.

The decision by U.S. District Court Judge Stephen Wilson in Los Angeles is a blow to the efforts of the music and movie industry to rein in widespread online copying, blamed for a significant decrease in sales and for widespread copyright infringement.

The ruling came in a suit brought by the Recording Industry Association of America against file-sharing services Grokster and Morpheus, popular successors to the now-defunct Napster service. Among the RIAA's members are labels owned by

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Unlike Napster, the file-swapping services provided only software, not the servers on which the songs were held. Wilson said the services could not be shut down because they didn't control what the software was used for, even if they knew it was being used illegally.