Adware (advertising-supported software) is any software application that plays, displays, or downloads advertising content to a user’s computer.
Typical features are pop-up windows or banners, changes to home page and search engine settings in the web browser, and so forth. Some adware is installed with the computer-user’s permission: for example, during the installation of a legitimate application with which the adware is bundled. This is the case with various dubious toolbars. Nowadays, it is difficult to strictly distinguish between adware, spyware and other potentially unwanted applications (PUAs).