(
Potentially
Unwanted
Program) An application that is installed along with the requested application. Also called a "barnacle," in most cases, PUP is spyware, adware or other unwanted software.
Not Malware?
What makes a PUP different than regular malware is the fact that the end user license agreement (EULA) may actually inform the user that this additional program is being installed. Considering hardly anyone ever reads the license agreement, the distinction is a subtle one (see
EULA). See
spyware,
adware and
malware.