The GPL gives you about as much protection as you could want. The 'viral' nature of the license ensures that, should they wish to distribute any program based on your code, they must provide that program to users under the terms of the GPL.

So if you provide them with the source under the GPL (unlike the BSD license), they have to provide it to others under that license, and part of the GPL says you have to provide the text of the license: 

1. You may copy and distribute verbatim copies of the Program's
source code as you receive it, in any medium, provided that you
conspicuously and appropriately publish on each copy an appropriate
copyright notice and disclaimer of warranty; keep intact all the
notices that refer to this License and to the absence of any warranty;
and give any other recipients of the Program a copy of this License
along with the Program.

[download]

It's all there in the GPL. It's good readin'.

In reply to Re: Licensing your software by arturo
in thread Licensing your software by Jouke

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