A seemingly minor legal victory in the US for a physics professor interested in open-source software and model trains looks like becoming a turning point for the 'free' software movement.

The ruling in a Washington appeal court effectively means that the simple fact of a developer giving away his software for free does not mean others can do as they wish with it.

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The appeal came after a case in which a physics teacher, Robert Jacobsen, lost the initial ruling over claims that a commercial business had violated the open-source licence under which software for controlling model trains had been distributed.

Jacobsen believed that reusing the open-source program without credit in both commercial train software and a later patent filing was illegal. When the original judgement went against him, he filed an ultimately successful appeal.

Creative Commons

Aside from proving a point about how to program toy trains legally, the verdict means all forms of non-fee-based licences now have full protection.

Creative Commons (CC) licences, as used by Wikipedia and many others, have to be respected just as much as entirely closed licences.

Writing on his personal blog, CC founder Lawrence Lessig said: "So, for non-law geeks, this won't seem important. But trust me, this is huge.

"The Court has held that free licences set conditions on the use of copyrighted work. When you violate the condition, the licence disappears, meaning you're simply a copyright infringer."

In other words, anyone reusing open-source software or other intellectual property without respecting the licence conditions is in for a rough ride, regardless of how 'free' they thought it was.