Open Source and the GNU General Public License

The open-source concept has many variants, but Microsoft has singled out one for particular criticism: The GNU General Public License (GPL). Linux and many of the applications that run on it are covered by this software license, originally created by the nonprofit Free Software Foundation for its GNU (“GNU’s not Unix”) project to develop a free Unix-like operating system.

Any software product covered by the GPL must be publicly available in source code form. However, the most striking provision of the GPL is what Microsoft has called its “viral” property: if a software product incorporates components covered by the GPL, that product itself is subject to the GPL and the product’s source code must be made available under the GPL’s terms. If a developer writes an application and distributes it with Linux, the developer must also publish the source code of the application.

Note that while the GPL prohibits distribution of GPL-covered components in a closed-source product, developers may create closed-source products that interact with software covered by a GPL through an API. This means they can, for example, write Linux applications and device drivers without distributing the source code for these products. Also, the GPL does not require vendors to distribute source code for free: vendors such as Red Hat Software can and do charge a fee for distributing products covered by a GPL. However, the provisions of the GPL mean that users can then redistribute those products, if they wish.