The High Court has thrown out an appeal by some of the world's biggest media companies to stop internet piracy after it excused Australian service provider iiNet from policing unauthorised downloads.

A group of 34 international and Australian companies, including industry heavyweights Warner Bros, Disney and the Seven Network, had alleged that iiNet had authorised the infringement of their copyright when its customers downloaded movies and television programs.

The movie companies had argued that iiNet had the power to prevent its customers from infringing copyright by issuing warnings and suspending or terminating customer accounts.

However, the High Court found that iiNet had no direct technical power to prevent its customers from using the BitTorrent file-sharing system to infringe copyright.

"Rather, the extent of iiNet's power to prevent its customers from infringing ... copyright was limited to an indirect power to terminate its contractual relationship with its customers," the court said.

iiNet chief regulatory officer Steve Dalby said while the company did not support illegal downloading, it was not its role to monitor or punish the behaviour of its customers by terminating internet access.

"It's not legal for us to look at what you're doing online anyway and secondly we don't have a responsibility to be the judge, jury and policeman who is working out what our customers are doing and trying to stop it and control it," Mr Dalby said.

Australian Federation against Copyright Theft managing director Neil Gane said internet service providers needed to play a central role in preventing online copyright infringements.