In what it is billing as an epic tale of good versus evil, Hollywood has launched a fresh round of legal cases against internet pirates who share films online.

The Motion Picture Association of America (MPAA), which represents America's giant studios, said it had acted on the US Supreme Court?s recent ruling that peer-to-peer file sharing networks can be held accountable for illegal online film distribution.

Users of peer-to-peer networks such as Grokster are able to browse millions of audio and video files on the internet. The files can be freely downloaded from the computers of other users, a practice which the film and music industries argue has hit their sales.

A recent Smith Barney study estimated that the film industry will lose up to $5.4 billion this year due to piracy.

If found guilty, people accused by the MPAA of piracy could face fines of up to $150,000 under copyright laws and prison sentences of up to ten years under federal legislation.

"Internet thieves be warned: You can click but you can?t hide," John Malcolm, the MPAA's director for worldwide anti-piracy, said.

"We won't stand by while people steal valuable copyrighted material with no regard whatsoever for the law or for the rights of creative people to be paid for their efforts."

However, some commentators have questioned the film industry's stance, pointing out that films such as Star Wars III, The Revenge of the Sith have beaten box office records despite pirate copies being available on the net within hours of their release.

Whether file-sharing technologies, which do not rely on central servers, will ever be contained has also been questioned.

The "collection of networks and technologies used to share digital content" was christened the "darknet" in a paper written by Microsoft engineers.

Despite the money spent to counter piracy, the experts concluded that the practice "will remain popular and become more widespread".

The MPAA has launched six rounds of legal action since November. Its decision to target individuals echoes action by the British music industry. It was announced yesterday that record companies are taking alleged pirates to court for the first time in Britain as they seek compensation for songs being illegally distributed over the internet.

The MPAA has argued that "moviemaking is an inherently risky business" and that piracy risks future investment. The organisation claims that only 1 in 10 American films breaks even through domestic exhibition and that 4 in 10 never recoup the original investment.

The average major studio film costs around $100 million to produce, market and advertise. "No other nation in the world risks such immense capital to make, finance, produce and market their films," the MPAA says on its website.

"We will go as many rounds as is necessary until people get the word that the online distribution of stolen movies is illegal and harmful to the people who use their talents to create movies that are enjoyed around the world," Mr Malcolm said.