Other examples of proprietary malware
Malware means software designed to function in ways that mistreat or harm the user. (This does not include accidental errors.)
Malware and nonfree software are two different issues. The difference between free software and nonfree software is in whether the users have control of the program or vice versa. It's not directly a question of what the program does when it runs. However, in practice nonfree software is often malware, because the developer's awareness that the users would be powerless to fix any malicious functionalities tempts the developer to impose some.
This page lists web sites containing proprietary JavaScript programs that spy on users or mislead them. They make use of what we call the JavaScript Trap. Of course, many sites collect information that the user sends, via forms or otherwise, but here we're not talking about that.
Many web sites snoop on information that users have typed into a form but not sent.
A research paper that investigated the privacy and security of 283 Android VPN apps concluded that “in spite of the promises for privacy, security, and anonymity given by the majority of VPN apps—millions of users may be unawarely subject to poor security guarantees and abusive practices inflicted by VPN apps.”
Following is a non-exhaustive list of some proprietary VPN apps from the research paper that tracks users and infringes their privacy:
E-books can contain JavaScript code, and sometimes this code snoops on readers.