A U.S. Circuit Court of Appeals decision has upheld the binding provisions of open source licenses, saying to fail to abide by their terms makes the user an infringer of their inherent copyright protections.

Until the decision in Jacobsen vs. Katzer was issued Wednesday, it wasn't clear whether a court of law would regard an open source license as being capable of imposing enforceable copyright restrictions on the use of computer code.

The Circuit Court of Appeals cited Stanford professor Lawrence Lessig's Creative Commons license and as well as Jacobsen's use of the Artistic License in saying that their provisions constitute a form of copyright.

"It's a fantastic win. Bob Jacobsen and I are very pleased with this result," declared Victoria Hall in an e-mail to InformationWeek. Hall represented Jacobsen in the case. "For non-geeks, this won't seem important. But trust me, this is huge," wrote Lessig on his blog Wednesday.

Open source licenses, particularly the GPL from the Free Software Foundation, reverse the established doctrine of copyright. They give away the right to use code, provided you abide by their provisions to make any changes available to other users. The opposite case, where you do not have the right to use material without paying for it, has a rich body of copyright case law. The open source licenses do not, and it has not been clear how the courts would decide the issue once it came before them.

The first decision in U.S. District Court for Northern California last Aug. 17 went against open source advocates. Jacobsen, a creator of open source model railroad control software, had been billed by Matthew Katzer, a commercial seller of similar code, for each free download that Jacobsen's project had allowed. The bill came to $203,000. Jacobsen, sued for a declaratory judgment that his open source code did not infringe Katzer's company's code.

The lower court ruled that the provisions of the Artistic License didn't protect Jacobsen. It was a stunning setback for all open source licenses and opened other projects to potential challenge. The Circuit Court of Appeals reversed that decision Wednesday and sent it back to the district court.