ncreasing legal action in the United States over piracy on YouTube, the video-sharing website, could set the scene for a test case against a British bootlegger, lawyers said. In the latest move, Twentieth Century Fox has demanded that YouTube reveal details of an American user who posted episodes of 24 and The Simpsons on the site. With analysts suggesting that relationships between YouTube and content owners could be deteriorating over piracy problems, lawyers are warning parents to be cautious about their children uploading bootlegged material. Struan Robertson, a senior associate with Pinsent Masons and the editor of out-law.com, the technology law website, said: “Many seem to be under the impression that using, for example, a pop song as the backing track to an amateur video is lawful. It is not.” He added: “We are likely to see action against an individual in the UK — a test case which will send out a message that it is not OK to use copyrighted material on the web. We have seen in it the music industry; it is not hard to predict it will happen in the TV industry.” The move by Twentieth Century Fox, the television group owned by News Corporation, parent company of The Times, underlined the tensions between content owners and so-called Web 2.0 sites, which depend on users uploading content to drive advertising revenues. YouTube, bought by Google last year for $1.65 billion, records more than 100 million video downloads a day. How is someone posting a clip or using a song as background music for an on-line clip they display at no personal profit the same as bootlegging? More often than not it generates interest in the band or TV show. NBC found that out after "Lazy Sunday" became a viral video and instead of suing joined forces with YouTube to promote NBC shows. Why don't the rest of these companies get it?