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.
In non-technical terms, 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.
It transpired that Matt Katzer and KAM Industries copied open source code from Robert Jacobsen and JMRI and then went to market it as his own.
See the BBC article here
Robert Jacobsen and JMRI news here
Matthew Katzer and KAM Industries here