Some thoughts on the BSD license

writes some interesting things… which I excerpt:

4.2 Clause 3 simply talks about Redistributions of source code. A distribution of modified source is a distribution of source code, so clause 3 applies a copy of these terms must be included with the modified source code. The wording does not support identification of a specific subset of the source code (ie the portion which is unmodified) for the license to apply to. Assuming our analysis above applies, then by including the license terms with the modified source code will make those terms (in particular, the rights to distribute and use in clause 2) apply to the whole of the modified source code as redistributed.

6. Can BSD Code be Licensed Under a Different License/Closed Source License? 6.1 We asserted above the collective wisdom that BSD code can be licensed under other licenses. There does not appear to be any basis for this wisdom in the terms of the license. Further, the terms of the BSD license do not appear to allow more restrictive licensing terms. This is not to say that the BSD terms forbid them. Rather, the BSD's usage and distribution rights are so broad, that additional (parallel) restrictions would appear to be ineffective.15 There is not even any basis on which modifications to the code can be used to leverage a different license16 because, as we have concluded above, (if part of a redistribution) those parts which are the original with or without modification must be licensed under the BSD terms.

(d) when a company incorporates BSD code into some software, then (to the extent the binaries are modifications of that BSD code) the company is, by assumption, required to license that software (including their own modifications and the source code for their modifications) under the terms of the BSD. We saw above that this does not mean that the source code must be released at all. However, what of the situation where the source code subsequently becomes available? If that was the case, would there be no copyright infringement for copying and distributing that source code? This is discussed further below;

9.3 We must therefore pose the question can an employee (or, more likely, an ex- or soon-to-be-ex employee) who has access to the modified source code disclose that source code to others if they acquire a copy of the released BSD binary (i.e. as released by the organization)? Even without this requirement, if the license of a binary version can affect the confidential nature of the source code for that version, then, depending on the timing, this may affect the ability to apply for patents which relate to the source code version.