I have come across a book that claims that alterations and augmentations to GPL works can be kept close-source as long as these are not redistributed into the wild. Therefore, customizations of websites deriving from GPL packages need not be released under the GPL and developers can earn profit on them by offering their services to their clients while keeping their GPL-based code closed source at the same time.

(cf. Chapter 17 of WordPress Plugin Development by Wrox Press).

I've never realized this, but essentially, by putting restrictions on redistributable code the GPL says nothing about what can and cannot be done with code which is kept private in terms of the licensing model.

Have I understood this correctly?

  • An interesting point is whether sample code showing how to communicate with SaaS-deployed GPL-derivative code would fall under GPL and require release of source code corresponding to the the undistributed GPL-derivative binaries. – Ben Voigt Mar 24 '14 at 20:37

Yes, you have understood that correctly. To address this loophole in the GPL license, the Affero GPL licence has been created, which considers using the software as part of a website as being a distribution of that software.

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    -1 for calling that "a loophole". – vartec Jun 24 '13 at 11:21
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    @vartec: What better name would you use for the possibility to contravene the spirit of the GPL without violating it. – Bart van Ingen Schenau Jun 24 '13 at 11:33
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    Naming that "loophole", you're suggesting that doing so is somehow morally ambiguous to say the least. It is not. GPLv2 is clear cut case of distribution license. The fact that The-Man-In-Tinfoil-Hat changed his mind after 15 years, does not mean that "the spirit of GPLv2" somehow retroactively changed. – vartec Jun 24 '13 at 11:40
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    @vartec: Please check your facts. There is an Affero license based on GPLv2, to "close a perceived application service provider 'loophole' (the 'ASP loophole') in the ordinary GPL, where by using but not distributing the software, the copyleft provisions are not triggered." Only GPLv1 (which pre-dates the widespread use of the internet) does not have a corresponding Affero license. – Bart van Ingen Schenau Jun 24 '13 at 12:00
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    @vartec: I agree that Affero v1 is a separate, incompatible, license from GPLv2, but it was expressly created because some people were concerned about the possibility to provide services with GPL-derived software without making the software itself available to the users and that is considered a loophole in the GPL (also v2) by them because it violates the spirit of the GPL, but not the letter. – Bart van Ingen Schenau Jun 24 '13 at 13:29

Copyright law questions are by definition off topic, and the answers you can get here are by definition untrustworthy.

However, you are basically right: the purpose of copyright is to restrict redistributing things. The author is allowed to do it, others, by default, aren't. Therefore, the author can't restrict your freedom to act if you don't redistribute anything that he has copyright on.

Note that the precise extent of what "redistributing" means ('give' it to your backup system? to a friend? to the employees of your company?) would have to be tested in court, like anything related to civil or criminal law, and AFAICT it hasn't been. (For perspective: where I live, even the fundamental question of whether EULAs are legally binding or not has never been been clearly decided.)

  • Like copyright, the right to publicly perform a work is also restricted. – Ben Voigt Mar 24 '14 at 20:29

GPL up to version 2 is distribution license, so if GPLv2 is the one used you understand that correctly. Basic idea of GPL is that you have to provide the source code to everyone that you provide with binaries. In your case you don't provide binaries to anyone but yourself.

However, starting with GPL version 3, there are more restrictions. One of them is optional Affero clause, which closes what they call a "SaaS loophole". GPLv3 with Affero clause is often referred to as AGPL.

Other restrictions relate to software patents (most likely not your case), tivoization (i.e. distributuion of hardware with unmodificable GPL code, so not your case either), and DRM implementation.

This is exactly the reason why for example Linux kernel is GPLv2 and will never switch to GPLv3.

  • -1 for calling that a "loophole". Ok, just kidding. But I should, since you essentially did the same in another answer. – Andres F. Jun 24 '13 at 13:06

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