Many spyware programs display advertisements. Some programs simply display pop-up ads on a regular basis. Others display ads in response to specific sites that the user visits. Spyware operators present this feature as desirable to advertisers, who may buy ad placement in pop-ups displayed when the user visits a particular site. It is also one of the purposes for which spyware programs gather information on user behavior.
Many users complain about irritating or offensive advertisements as well. Many spyware advertisements use animation or flickering banners which can be visually distracting and annoying to users. The term adware frequently refers to any software which displays advertisements, whether or not the user has consented. Adware is classified in the sense of advertising-supported software, but not as spyware. Adware in this form does not operate surreptitiously or mislead the user but is intended to provide the user with a specific service.
Although most adware is spyware in a different sense for a different reason, it displays advertisements related to what it finds from spying on you. Thus the user receives many pop-up advertisements based on browsing. Other spyware behavior, such as reporting on websites visited, occurs in the background. The data is used for targeted advertisement impressions.
The prevalence of spyware has cast suspicion upon other programs that track Web browsing, even for statistical or research purposes. Many of the adware distributing companies are backed by millions of dollars of adware-generating revenues.