A couple of weeks ago, a U.S. federal court ruled that the GNU General Public License (GPL) is an enforcable license. As this is a potentially important legal event - at least in the U.S. - it's been discussed both on Hacker News and on Reddit's programming subreddit.
The case in question concerns a South Korean software company called Hancom, which integrated the PDF toolkit Ghostscript developed by California-based Artifex into its office suite without adhering to the conditions of the license it was made available under.
Originally written by Richard Stallman and the Free Software Foundation, the GPL gives users what the organization regards as the prerequisites for being called "free software" - "the four essential freedoms":
- The freedom to run the program as you wish, for any purpose (freedom 0).
- The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this.
- The freedom to redistribute copies so you can help your neighbor (freedom 2).
- The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.
Note that, despite what some might believe, the GPL does not require the software in question to be gratis (or "free as in beer") - only libre (or "free as in speech").
In what is known as a reciprocity requirement, the conditions of the GPL also stipulate that any derivative work based upon GPL-licensed original work must also be licensed under the GPL.
In the case of Hancom vs. Artifex, Ghostscript was in fact dual-licensed - alternatively made available under a commercial license (i.e. for a fee), for those that for some reason or another do not wish to adhere to the GPL.
As Hancom did not make any changes freely available (as per the GPL), they were effectively "going down the closed-source commercial license lane but without paying a dime" and infringing copyright. This prompted creators Artifex to unsuccessfully demand backdated license fees, before suing Hancom in a California district court.
The gist of the matter is that Judge Corley denied Hancom's motion to dismiss the case on the grounds that the company didn't sign anything - thus the license wasn't a "real contract". In doing so she set the precedent that software licenses can be treated like legal contracts - even though the FSF has historically not necessarily agreed.
The official court records are available here.