- The freedom to run the program as you wish, for any purpose (freedom 0). - The freedom to study how the program works, and change it so it does your computing as you wish (freedom 1). Access to the source code is a precondition for this. - The freedom to redistribute copies so you can help others (freedom 2). - The freedom to distribute copies of your modified versions to others (freedom 3). By doing this you can give the whole community a chance to benefit from your changes. Access to the source code is a precondition for this.

If the users don't control the program, the program controls the users. With proprietary software, there is always some entity, the developer or “owner” of the program, that controls the program—and through it, exercises power over its users. A nonfree program is a yoke, an instrument of unjust power.

In outrageous cases (though this outrage has become quite usual) proprietary programs are designed to spy on the users, restrict them, censor them, and abuse them. For instance, the operating system of Apple iThings does all of these, and so does Windows on mobile devices with ARM chips. Windows, mobile phone firmware, and Google Chrome for Windows include a universal back door that allows some company to change the program remotely without asking permission. The Amazon Kindle has a back door that can erase books.

Consider GNU Objective C. NeXT initially wanted to make this front end proprietary; they proposed to release it as .o files, and let users link them with the rest of GCC, thinking this might be a way around the GPL's requirements. But our lawyer said that this would not evade the requirements, that it was not allowed. And so they made the Objective C front end free software.

Those examples happened years ago, but the GNU GPL continues to bring us more free software.

What was claimed to be the first US lawsuit over a GPL violation concerned use of BusyBox in an embedded device. The lawsuit,[17] case 07-CV-8205 was filed on September 20, 2007, by the Software Freedom Law Center (SFLC) on behalf of Andersen and Landley against Monsoon Multimedia Inc., after BusyBox code was discovered in a firmware upgrade and attempts to contact the company had apparently failed. The case was settled with release of the Monsoon version of the source and payment of an undisclosed amount of money to Andersen and Landley.

After several attempts for an off-court solution, the question was finally settled by the parties, restoring the correct license, and the other issues.