IANAL, but the typical open source licenses are written so that once source code has been released under the license, it can't be retroactively revoked. The copyright owner can adopt a new license for new changes, effectively forking his own work under a more limited license.<p>This has happened to many open source projects. Some examples off the top of my head:<p>- AntiGrain Geometry, a high-quality rasterizer library, switched from LGPL to plain GPL at version 2.5. The previous version has been developed further by other parties than the original author.<p>- Symbian, a smartphone OS that used to be the #1 in marketshare a surprisingly short time ago, was released by Nokia under an Apache license. Once the company gave up on the idea of having the OS developed in the open, they relicensed the code under a far more limiting custom license.