The US federal appeals court move overturned a lower court decision involving free software used in model trains that a hobbyist put online.
The court has now said conditions of an agreement called the Artistic Licence were enforceable under copyright law. Legal experts have said the distinction is important since under federal copyright law a plaintiff can seek statutory damages and can be more easily granted an injunction than under contract law.
The ruling has implications for the Creative Commons licence which offers ways for work to go into the public domain and still be protected. These licenses are widely used by academic organisations like MIT for distributing coursework, scientific groups, artists, movie makers and Wikipedia among others.