Software that is designed to launch advertisements, frequently pop-up ads, on a user’s computer and/or to redirect search results to promotional Web sites. Adware programs are often built into freeware or shareware programs, where the adware creates an indirect ‘charge’ for using the free program. Sometimes a trojan can silently download an adware program from a Web site and install it onto a user’s machine.
Hacker tools, or Browser Hijackers, can also download an adware program by exploiting a web browser’s vulnerability. Browser Hijackers may tamper with the browser settings, redirect incorrect or incomplete URLs to unwanted Web sites, or change the default home page. They can also re-direct a user’s searches to “pay-to-view” (often pornographic) Web sites.
Typically, many adware programs do not leave any marks of their presence in the system: they are not listed on Start | Programs; they add no icons to the system tray; and they don’t show up on the task list. In addition, adware programs seldom provide an uninstallation procedure, and attempts at manually removing them frequently result in failure of the original carrier program.