Adware

Taken from Savvy Security

6. Definition: Adware is usually a software element (a program) whose purpose is to generate revenue for the owner of an application, service, or website. These ads may be in the form of popups, streaming messages, whole areas of a web page, through a bar on the screen, or installed and played when a user downloads software.
   
   What's malicious about adware is that the underlying code within these ads may track a user’s personal behavior (e.g., which ads are clicked the most) and pass on the information to 3rd parties for commercial purposes, which, without the user's awareness and explicit consent, is illegal in certain states and countries.
   
   Reason for the name: Abbreviation of "advertisement malware".
   Propagation: Adware might illegally collect data or perform other unaware of or undesired actions when a user interacts with the ad (hovers over it, clicks it, plays it, etc.)
   Examples of well-known adware types: Zango and Fireball.