View source for PUP

PUP is an acronym for Potentially Unwanted Program.  A PUP is similar to a virus or malware.  The term "grayware" is often used to describe PUP software.  A PUP is a program that is typically unwanted, despite the possibility that users accidentally consented to download it by way of not manually opting out.  In other words, there was a checkbox to untick, or some "fine print" somewhere in the installation process for another program that the user didn't notice and thus got slammed with additional software.

PUP software includes spyware, adware, and other types of malware that are often downloaded in conjunction with a program that the user wants.  You wanted to download and install Program A but did not realize that it snuck in Program B, C and D without you noticing.  It is Programs B - D that are the PUPs.  

The McAfee anti-virus company takes credit for coining the acronym PUP.  McAfee differentiates PUPs from other types of malware, such as viruses, Trojans, and worms, which can be safely assumed to be unwanted by the user.

PUPs tend to come bundled with free software or free apps that you (the user) downloads.  To avoid getting slammed with PUPs on your computer you really do have to pay attention to the installation process of that software you just downloaded.  Each PUP first appears as a trap in the desired program’s installation wizard.