WWW- America’s biggest media companies have accused Google of knowingly encouraging copyright theft by suggesting to illegal movie download sites that they place adverts to appear in response to search terms such as “pirated” and “bootleg”.

Rupert Murdoch’s News Corporation, Viacom, Walt Disney and Time Warner are among a group of leading television and film producers that has complained about a lack of controls at Google.

Their anger centers on a case going through the courts in New York state surrounding five defunct movie download websites with names such as TheDownloadPlace.com, MoviesAdvance.com and EasyDownloadCenter.com.

Run until last year by two 26-year olds in Missouri, the sites allowed users to download Hollywood hits such The Incredibles, Charlie and the Chocolate Factory, Meet the Fockers and Mr & Mrs Smith in their entirety.

Legal documents allege that Google accepted adverts and endorsed “sponsored links” from the websites’ operators, Brandon Drury and Luke Sample. The company even offered credit on payments from the duo.

Google is accused of suggesting to the pair that their adverts appear when people enter various movie titles on its search page – or when terms are entered such as “bootleg movie download”, “pirated” and “download harry potter movie”.

The row is a sign of deteriorating relations between media companies and Google. For months television companies and film studios have been struggling to agree deals to control the way their content is used on YouTube – the video-sharing site acquired by Google last year.

Google’s main source of income is a fee paid by advertisers whenever anyone clicks on a sponsored link. The company routinely helps clients choose suitable search terms to prompt their links.

The firm, which trades under the slogan “don’t be evil”, assured the media companies on Friday that it would tighten its systems to prevent a recurrence of sponsored links to bootlegging sites.

A Google spokesman said: “We prohibit advertisers from using our advertising program to promote the sale of copyright-infringing materials. Hundreds of thousands of advertisers responsibly abide by our ad content policies and we’re committed to preventing those who don’t from using our program.”

The broader question of controlling content on Google’s network of websites remains contentious. YouTube users routinely upload clips from popular shows.

News Corp’s Fox network last month got tough with YouTube by filing a subpoena demanding the name of a subscriber who posted entire episodes of the television series 24 and The Simpsons on the site. YouTube has since complied.

The media firms would prefer to use YouTube as a shop window offering a controlled selection of tasters from their movies and television shows.

In a step towards such control, News Corp’s MySpace social networking site yesterday announced plans to block unauthorised music and videos using technology from a company called Audible Magic. The software allows MySpace to compare uploads with a database of copyrighted material and to block content that shows a match.

In a pilot, MySpace intends to use the technology to filter out any clips by Universal Music’s roster of artists – which includes the Black Eyed Peas, Miss Dynamite and Snow Patrol.

Steve Weinstein, an analyst at Pacific Crest Securities, said neither the media firms nor Google wanted to get into the kind of bitter copyright face-off that led to the downfall of the once ubiquitous music sharing site Napster. But he said a solution to the problem was elusive: “The studios don’t know and Google doesn’t know how best to make this work yet.”

Backstory: Downloading films has never been easier, thanks to the sheer number of services available. The most prominent is BitTorrent. Users download software and find a “tracker” site which tells them where the movies they are looking for are stored. Despite some high-profile closures, web services continue to act with impunity. One of the most famous is The Pirate Bay, run by a Swedish group that believes copyright is wrong. After police raids, it announced that it was raising funds to buy its own island.