The term Potentially Unwanted Programs was created by anti-virus maker McAfee because, they didn't wanted to classify these programs as spyware because of the fear of legal actions that could be taken against them by the makers of these Potentially Unwanted Programs.
Potentially Unwanted Programs include adware, spyware, web browser hijacker and toolbars. Some of these programs are creating by legitimate organizations and used as a marketing tool and can be difficult to remove after installation.
Potentially Unwanted Programs are usually bundled with free software and have an option to install or not to install. The install options are selected by default and, most users will quickly bypass or overlook these options without realizing that they have consented to installing these unwanted programs.
Free software makers usually monetize their software by bundling them with Potentially Unwanted Programs.
It is recommended that you choose “Custom Installation” when installing free software instead of, “Typical Installation” which is always selected as the default.
Choosing “Custom Installation” allows you to choose, if any, which additional programs to install.