A US federal judge in Washington wrote that a suspected internet pirate should not be prosecuted solely because his computer's IP address was identified by a film studio. The landmark opinion may tip the fortunes of defendants in similar situations.

The Hollywood executives behind the movie ‘Elf Man’ filed a lawsuit against hundreds of people, alleging that they were guilty of copyright infringement because their internet protocol (IP) address was found to have illegally downloaded the film. An IP address can be likened to a computer's online fingerprint; each is unique to the machine it originates from.

Copyright holders seeking to take offenders to court often put fake movie files online, record the hundreds or thousands of IP addresses that download it, and then provide that information to the courts in an attempt to identify and sue hapless users on the other side of the screen.

The studio argued that “the defendants either (a) downloaded the pirated film themselves, or (b) permitted, facilitated, or promoted the use of their Internet connections by others to download the film,” according to TorrentFreak.

Washington District Judge Robert Lasnik said this week that the rationale is insufficient, in part because it begins with the assumption of guilt. Ruling on a motion to dismiss the claim, Lasnik sided with the defendants because the conditions described in complaint section b were overly vague.

“[The movie studio] has actually alleged no more than the named defendants purchased Internet access and failed to ensure that others did not use that access to download copyrighted material,” the judge wrote.

Lasnik also said that there was no proof that the person who could wind up facing a lawsuit was in fact the person who chose to download the copy of ‘Elf Man.’

“Simply identifying the account holder associated with an IP address tells us very little about who actually downloaded 'Elf Man' using that IP address,” he wrote. “While it is possibly that the subscriber is the one who participated in the BitTorrent swarm, it is also possible that a family member, guest, or freeloader engaged in the infringing conduct.”

Other judges presiding over similar cases in the past have agreed with Lasnik, creating a precedent that has required copyright enforcers to narrow down their list of suspects before attempting to launch a case.

Last year, a Sydney-based law firm revealed that courts in both Australia and the US have refused to turn over personal details of internet users who downloaded content without permission.

“For example, in an office or at home, where there is a WiFi connection, only one IP address will be allocated to that wireless connection. This means that every user of each device (computer, iPad, iPhone, etc) connected to that WiFi connection will use the same IP address. Even a random passerby accessing the WiFi network would be using the same IP address,” lawyers from Marque Lawyers wrote, as quoted by TorrentFreak.

“This decision makes a lot of sense to us If it holds up, copyright owners will need to be a whole lot more savvy about how they identify and pursue copyright infringers and, perhaps, we’ve seen the end of the mass 'John Doe' litigation.”