Adware, or advertising-supported software, can be bundled with, or built into, a program, as well as a stand-alone application. This type of program will display advertisements and can also download advertising materials to a computer once it is installed. Adware can generate popup advertisements, advertising banners on a browser, add a toolbar to a browser, or even direct search results to targeted pages.

Popups can be very intrusive and annoying, and some are not family friendly and display inappropriate material. Adware popups can be very deceptive, in some cases of adware popups the “no,” “cancel” or “close” options within the popup will actually trigger a “yes” or “install” response instead. It is always best to close a popup window using the close option in the top right hand corner of the window (the little red x).

Toolbars that are installed by adware are generally search engine based, and in the worst malicious cases, they cannot be turned off. Some of the more malicious adware toolbars can even disable other legitimate toolbars that may have been installed previously. The search results displayed from the toolbar may have restricted results, where they will only display the sponsored results. Sponsored results are from companies that pay for their positioning.

Most adware programs are generally used to generate a profit, making it is easy to see why it is found with so many “free” programs, trial versions of software, and Shareware. Since a free program does not cost a user, the company doesn't make too much money from a user, therefore must rely on adware programs to gain a profit. So long as the adware included with a program is described in the Terms of Use or End Users License Agreement (EULA), and does not go outside it's description of the softwares functions, it is completely legal.

One of the things that can make adware dangerous is that it can pass on a users personal data to third parties. Adware usually tracks browsing habits through cookies, which were originally placed on the computer by a legitimate site, for uses such as keeping your shopping car inventory. However, some of these cookies may contain too many personal details, which could end up in the wrong hands or be sold to other companies. This transferring of information is highly criticized by privacy advocates. Adware programs start to cross into the spyware realm when they track user information without a users consent, especially when the information gathered can be easily accessed by a third party.

The US government has strict rules about cookie use, but not everyone follows the rules, and people will try to get away with a lot of things, at least until they get caught. To be legitimate adware, the company must reveal to a user exactly what they are doing, usually described in a EULA or Terms of Service. The company must also gain users consent before it downloads, installs and runs it's advertising software.