The Supremes unanimously overturned a ruling that barred the film and music industries from suing Internet services such as Grokster on which users can exchange songs and movies.
A District Court and the Court of Appeals had previously held that the defendants' software was capable of lawful use and so they could not be held liable for what their users get up to.
But the Supremes weren't having any of it and sided with the big boys.
Wrote Justice David Souter: "One who distributes a device with the object of promoting its use to infringe copyright ... is liable for the resulting acts of infringement by third parties using the device, regardless of the device's lawful uses."
It looks like the Supremes decided the file-sharing networks promoted the technology as a way of illegally sharing copyrighted files.
A key defence precedent was that set by the Sony Betamax judgement which found that it wasn't Sony's fault if folk used new-fangled video recorders to tape stuff off the telly.
The decision will send shockwaves through the Internet community. Reactions are expected shortly. µ
L'INQ
Ten Commandments