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 often exercise that power to the detriment of the users they ought to serve.
This page describes how various proprietary programs mess up the user's system. They are like sabotage, but they are not grave enough to qualify for the word “sabotage”. Nonetheless, they are nasty and wrong.
If you know of an example that ought to be in this page but isn't here, please write to <webmasters@gnu.org> to inform us. Please include the URL of a trustworthy reference or two to present the specifics.
Pearson's proprietary educational software did an experiment on real students, treating students differently to observe the results.
Microsoft is planning to make Windows impose use of its browser, Edge, in certain circumstances.
The reason Microsoft can force things on users is that Windows is nonfree.
Windows displays intrusive ads for Microsoft products and its partners' products.
The article's author starts from the premise that Microsoft has a right to control what Windows does to users, as long as it doesn't go “too far”. We disagree.
Microsoft inserts annoying advertisements inside of the File Explorer to nag users to buy subscriptions for the OneDrive service.
An upgrade package for Acrobat Reader silently alters Chrome.
Microsoft has started nagging users obnoxiously and repeatedly to install Windows 10.
Microsoft is tricking users into replacing Windows 7 with Windows 10.
Microsoft has made companies' Windows machines managed by the company's sysadmins harangue users to complain to the sysadmins about not “upgrading” to Windows 10.
Apple forced millions of iThings to download a system upgrade without asking the users. Apple did not forcibly install the upgrade but the downloading alone caused lots of trouble.
Adobe nonfree software may halt all other work and freeze a computer to perform a license check, at a random time every 30 days.
Microsoft has desupported all future Intel CPUs for Windows 7 and 8. Those machines will be stuck with the nastier Windows 10. AMD and Qualcomm CPUs, too.
Of course, Windows 7 and 8 are unethical too, because they are proprietary software. But this example of Microsoft's wielding its power demonstrates the power it holds.
Free software developers also stop maintaining old versions of their programs, but this is not unfair to users because the users of free software have control over it. If it is important enough to you, you and other users can hire someone to support the old version on your future platforms.
Oracle made a deal with Yahoo; Oracle's nonfree Java plug-in will change the user's initial web page, and default search engine, to Yahoo unless the user intervenes to stop it.
Microsoft is repeatedly nagging many users to install Windows 10.
Microsoft was for months tricking users into “upgrading” to Windows 10, if they fail to notice and say no.