From Ars Technica:

A federal appeals court has overruled a lower court ruling that, if sustained, would have severely hampered the enforceability of free software licenses. The lower court had found that redistributing software in violation of the terms of a free software license could constitute a breach of contract, but was not copyright infringement. The difference matters because copyright law affords much stronger remedies against infringement than does contract law. If allowed to stand, the decision could have neutered popular copyleft licenses such as the GPL and Creative Commons licenses. The district court decision was overturned on Wednesday by the United States Court of Appeals for the Federal Circuit.

According to “Condition or Covenant, and Why Should You Care?” from the Electronic Frontier Foundation, key point was whether ‘copyleft’ licenses — in this case, Artistic License 1.0 — are covenants or conditions (read the EFF article to learn the difference).

The court ruled that the license in question specified certain conditions that had to be satisfied in order for the user to be a licensee. In a nutshell: if you don’t meet those conditions, you are not licensed, and are violating the author’s copyright.

Related: Jacobson v Katzer decision [PDF Link]