Re: Would copying the theme of bbpress.org be illegal?
I believe the theme for this forum is available for download somewhere, it might even be Trent’s theme?
The GPL doesn’t work that way. The idea of “linking” is very compiler specific terminology, it doesn’t really apply to php scripts calling other php scripts.
Changing GPL code is OK and you can’t be forced to redistribute it (hand over source), but if you do, the source must be made available and the licensing must remain the same GPL license.