Adware is the general term applied to programs that either launch advertisements (often pop-up banners) or re-direct search results to promotional web sites. Adware is often built into freeware or shareware programs: if you download a freeware program, the adware is installed on your system without your knowledge or consent. Sometimes a Trojan will secretly download an adware program from a web site and install it on your computer.
Web browsers that aren’t up-to-date often contain vulnerabilities. Such browsers are vulnerable to hackers tools (often referred to as Browser Hijackers) that can download adware to your computer. Browser Hijackers may change browser settings, redirect incorrectly typed or incomplete URLs to a specific site, or change the default homepage. They may also redirect searches to pay-to-view (often pornographic) web sites.
Typically, adware programs do not show themselves in the system in any way: there will be no listing under Start | Programs, no icons in the system tray and nothing in the task list. They seldom come with a de-installation procedure and attempts to remove them manually may cause the original carrier program to malfunction.
