Imagine that you write some code, and offer it to the public under an open source license that requires that if someone distributes modified versions of the code, the modified versions also be open sourced. Now assume someone distributes modified versions of your code, but fails to open source the modified code.

Do you have a claim for breach of contract? Or for copyright infringement? Or both? And why should anyone other than a law professor care?

Copyright law and contract law are very different. The things you need to prove to win a case are different. Copyright law is federal, while contract claims fall under state law, which varies from state to state. Copyright damages will often be more expansive than contract damages. The standards for injunctive relief are different. The prevailing party in a copyright case can seek attorneys' fees, while the general rule in contract cases is that both sides bear their own attorneys' fees.

So it matters whether copyright or contract law applies.

And, truth be told, the hypothetical at the top of this post is not quite so hypothetical; it is very close to the facts in Jacobsen v. Katzer, a case concerning open sourced code from the Java Model Railroad Interface group. Today, the Federal Circuit vacated a district court decision [PDF] that had held that only contract law was implicated by the defendants' alleged breach of the open source license applicable to the JMRI code.

The court concluded that the key question was whether the parts of the agreement the defendants allegedly breached were mere covenants (things the defendants agreed not to do when they accepted the license), or also conditions of the license (things that must be satisfied in order for the defendants to be licensed at all). Because the license at issue went out of its way to state that licensees' obligations were "conditions," the court concluded that if the defendants were in breach, the plaintiff could sue for copyright infringement.

There are a lot of things in this opinion that the open source community should cheer. The opinion notes that open source software "can often be written and debugged faster and at lower cost than if the copyright holder were required to do all of the work independently," and points out that "[t]here are substantial benefits, including economic benefits, to the creation and distribution of copyrighted works under public licenses that range far beyond traditional license royalties." And the court emphatically concluded that "[c]opyright holders who engage in open source licensing have the right to control the modification and distribution of copyrighted material."

While we're pleased to see a panel of learned judges endorse the legal foundations of the open source software paradigm, the decision may also encourage proprietary software vendors who frequently fill their "end user license agreements" with restrictions that are denominated as "conditions" on the license.

If violating a "condition" in a EULA results in copyright infringement liability, what's to stop a software vendor from imposing conditions that are unrelated to copyright law (e.g. an agreement not to disparage the copyright owner, or to wear pink bunny ears on Tuesdays), or even antithetical to copyright law (e.g. a waiver of fair use rights)?

For a view of the dark side of "conditions" imposed in proprietary software licenses, consider the "thou shalt not run software we don't like" terms that Blizzard imposes on those who purchase World of Warcraft software, terms that recently were upheld in court despite a very astute amicus brief by Public Knowledge.

We're sure to see this issue come up again in future cases, so stay tuned.