A US jury is about to make a landmark decision as to whether an IP address can be used to identify a software pirate.
Cases bought and paid for by Big Content depend on identifying the IP address of machines, but experts have questioned whether the IP address is sufficient evidence because it identifies an internet connection rather than a person.
A porn company, Malibu Media, has instigated 349 mass lawsuits, 43 in Pennsylvania this year. Most of the cases are settled out of court because the company was armed with an IP address and it could threaten users with settlement demands.
But in one lawsuit, five of the anonymous defendants protested when their internet service providers were ordered to reveal their identities.
They accused Malibu Media of pursuing the cases "to extort settlements".
Judge Michael Baylson, of the Pennsylvania District Court, said that the accused claimed BitTorrent does not work in the manner the plaintiff alleges.
"A mere subscriber to an ISP is not necessarily a copyright infringer, with explanations as to how computer-based technology would allow non-subscribers to access a particular IP address," he said.
There is no reason to assume an ISP subscriber is the same person who may be using BitTorrent to download the alleged copyrighted material.
He said that a trial was needed "to decide who's right".
According to TorrentFreak the trial will set an important precedent.
If the jury agrees that the IP address cannot identify a user, then US courts will not be allowed to insist that addresses are handed over to copyright holders.
It will also mean that copyright holders will not be allowed to threaten users with expensive court cases without finding other methods of proof.