@ Downix
Just a correction.
The following is from the Preamble of the GNU GPL (Version 2, June 1991): (Bold emphasis is mine)
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"When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code
or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things"
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Section 2 of the licence reads:*****************
"You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:
a) You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.
b) You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.
c) If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License. (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.) "
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Nowhere in the licence do I find reference to a requirement of uploading to a CVS repository.
I neither find references to any timing requirements to make public any changes.
As long as the changed code is made available upon request under the same license there is no breach of the GPL.
As a matter of interest you might like to know that the whole concept of GPL is about to be challenged in court by SCO.
Read more about it
HERE.