Nonfree (proprietary) software is very often malware (designed to mistreat the user). Nonfree software is controlled by its developers, which puts them in a position of power over the users; that is the basic injustice. The developers and manufacturers often exercise that power to the detriment of the users they ought to serve.

This typically takes the form of malicious functionalities.

The “jails” are malicious operating systems that are designed to impose censorship of which applications the user can install. The image of the iPrison illustrates this issue.

These systems are platforms for censorship imposed by the company that owns the system. Selling products designed as platforms for a company to impose censorship ought to be forbidden by law, but it isn't.

This page lists a few jails, along with some of the methods they use to censor apps, and includes specific examples of apps that were blocked using this censorship power.