YouTube's recent US federal court victory against Viacom is being touted as a landmark for online file sharing – although there's still a risk the ruling could be overturned on appeal. Viacom, owner of Paramount, MTV, Comedy Central and Nickelodeon (among others), sued YouTube's owner, Google, for a billion dollars. It alleged YouTube violated the Digital Millennium Copyright Act because it knowingly hosted video material illicitly copied from movies and TV shows. Viacom further alleged that YouTube encouraged and profited from this behaviour. The Act requires the likes of YouTube to take down offending material when issued with the appropriate notice by the copyright holder, but doesn't require them to actively seek out such material. The judge said the Act includes a 'safe harbour' provision, designed to relieve websites from the burden of checking user-generated material before it's posted.Even at YouTube, where lots of people violate the law, "mere knowledge of the prevalence of (copyright violations) in general is not enough" to make the site liable, the judge said. He also noted that the current system can work well. For example, in February 2007, Viacom identified 100,000 videos that it said violated its copyrights. By the next day, "YouTube had removed virtually all of them," the judge said. The ruling also applied to other parties in the suit, including England's Premier Football League. "This is an important victory not just for us, but also for the billions of people around the world who use the web to communicate and share experiences with each other," Kent Walker, vice president and general counsel at Google, wrote on the Official YouTube Blog. Indicating that it would appeal, Viacom called the ruling "fundamentally flawed and contrary to the language of the Digital Millennium Copyright Act, the intent of Congress and the views of the Supreme Court"If that appeal succeeds, it would do incalculable damage to online multimedia, and open the way for a swathe of other, similar lawsuits. However, the courts may be unwilling to pass a judgement that would have such effects. "One of the biggest barriers to this is YouTube is just so damn popular now," said one US lawyer heavily involved in copyright cases. "No one judge is simply going to flip off the switch… judges will consider the impact of their ruling in any industry. And YouTube has become so embedded in the fabric of this country that it's hard to imagine any judge pulling the plug.