PUP is generally used to refer to programs that are accidentally or surreptitiously downloaded and installed, usually as an unexpected or unwanted side effect of installing something else.Most examples involve undesired toolbars, but this class of annoyance can be just about anything.Pop up blockers were created to prevent pop up windows from happening.
Virus detection is more typically data-based, looking for specific patters of data that indicate the presence of a virus.
In reality, the lines between spyware and other forms of malware tend to blur, although typically a protection solution for each is still required.
A virus is a computer program written by someone, with the presumed intent of spreading and causing grief.
The term was probably developed by people (like me) who didn’t want to keep writing out “viruses and spyware and adware and …” when writing about current internet threats.
PUP is an acronym that stands for Potentially Unwanted Program.