Caution remains the watchword for incorporation of “copyleft” software into proprietary software projects, as a German court has declined to provide insight into the reach of the influential free software license, the General Public License (GPL).

In a case that may have shed light on the GPL’s scope, Christoph Hellwig, one of the developers of the GNU/Linux operating system, claimed that VMWare, Inc., had violated the GPL by incorporating some of his software into VMWare’s virtualization software without making the commercial product subject to the GPL license. The court, however, dismissed Hellwig’s claim without reaching the question of how to determine whether incorporation of GPL code into other software subjects the overall product to “copyleft” terms of the GPL. The case had drawn worldwide interest last year, when it seemed on track to address that issue. The court instead ruled that Hellwig had not sufficiently proven his interest in the software in question, so the critical GPL interpretation did not arise.

“Copyleft” is the term applied to describe the mechanism the GPL uses to require that software freedom — as conceived by the license’s author, the Free Software Foundation — is respected when software under that license is reused and distributed. It requires that the reused software also be distributed under the terms of the GPL license, which, in turn, require that the software’s source code be made available so future users of the product can both understand how it works and modify it to suit their own purposes.

The GPL (in version 2, the more common, though not the most recent, version) applies its terms not only on the GPL code being incorporated, but on the project in which that GPL-covered code is being used. It provides the following:

You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the [code licensed under the GPL] or any part thereof, to be licensed as a whole ... to all third parties under the terms of [the GPL].

Hellwig claimed that portions of the code he wrote for GNU/Linux, licensed under these terms, were used in VMware’s product and as such, that product “as a whole” was required to be licensed under the GPL terms. The question of how strict or how loose this clause of the GPL would be interpreted is critical to any analysis of the circumstances under which software developments that are not to be treated as free and open-source software must avoid including and distributing any GPL-covered components. The Hellwig vs. VMware case had been expected to add a judicial interpretation to aid the analysis of how restrictive a proprietary software project needs to be on this point. As the court resolved it, however, the case provides no insight on this matter.

Corporate lawyers advising on this topic should note that headlines in general media stating that VMware won this case should not be misinterpreted as suggesting the case gives any support for the use of GPL-licensed code in proprietary software. It does not. The case simply stands for the proposition that Christoph Hellwig did not adequately prove his interest in the software in question.

Published reports indicate that the plaintiff is evaluating an appeal.