Spyware:

Generally refers to deceitful software that is secretly installed on a user’s computer and that monitors use of the computer in some way without the user’s knowledge or consent.  Most spyware tries to get the user to view advertising and/or particular web pages.

In regards to affiliate marketing, lots of spyware programs are written by affiliate [...]

Affiliate Fraud:

Bogus activity generated by an affiliate in an attempt to generate illegitimate, unearned revenue.

Commonly referred to as Black Hat activity, unfortunately there are lots of tactics that unethical affiliates can use to generate revenue.  Click fraud, redirects, adware, software programs, tool bars, etc.  There are many active affiliates out there that are working to [...]

Parasite:

Software that works on a person’s computer, typically without their knowledge or consent and without a visible interface.  It can include software that’s installed along with another application.

Parasites are pretty universally looked down upon amongst white-hat, legit affiliate marketers.  Recently there was a class-action lawsuit against Commission Junction for allowing affiliates using parasitic software to [...]