For the developers' and authors' protection, the GPL clearly explains that there is no warranty for this free software. For both users' and authors' sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions.

The GPL v3 license permits users of the code to: Use the code for commercial purposes: Like GPL v2, GPL v3 imposes no conditions on the internal use of the software.

The GPL is a free software license, and therefore it permits people to use and even redistribute the software without being required to pay anyone a fee for doing so. You can charge people a fee to get a copy from you. You can't require people to pay you when they get a copy from someone else.

For example, if a program consists only of original source code, or is combined with source code from other software components, then the custom software components need not be licensed under GPL and need not make their source code available; even if the underlying operating system used is licensed under the GPL, ...