Adware is a legitimate, non-replicating program designed to display ads to the end user, often based on monitoring of browsing habits, and often in exchange for the right to use a program without paying for it. Some types of adware can also contain spyware and can be classified as privacy-invasive software. Adware can slow down a computer by using RAM and CPU cycles, or slow down a user's Internet connection by using bandwidth to retrieve advertisements.
Advertising functions are integrated into or bundled with the software, which is often designed to note what Internet sites the user visits and to present advertising pertinent to the types of goods or services featured there. Adware is usually seen by the developer as a way to recover development costs, and in some cases it may allow the software to be provided to the user free of charge or at a reduced price. The income derived from presenting advertisements to the user may allow or motivate the developer to continue to develop, maintain and upgrade the software product. Conversely, the advertisements may be seen by the user as interruptions or annoyances, or as distractions from the task at hand.
Some adware is also shareware, and so the word may be used as term of distinction to differentiate between types of shareware software. What differentiates adware from other shareware is that it is primarily advertising-supported. Users may also be given the option to pay for a "registered" or "licensed" copy to do away with the advertisements.
Adware may also hijack the browser to redirect it to its own search engine, and/or restrict usage of Registry Editor, Command Prompt and Microsoft Configuration Utility. Adware can also download and install potentially unwanted programs (PUPs). Most adware comes from toolbars, which also usually hijack the browser.
- Adware on Wikipedia.