Most free software that is supported by advertisements. Common adware programs are toolbars that sit on your desktop or work in conjunction with your Web browser. They include features like advanced searching of the Web or your hard drive and better organization of your bookmarks and shortcuts. Adware can also be more advanced programs such as games or utilities. They are free to use, but require you to watch advertisements as long as the programs are open. Since the ads often allow you to click to a Web site, adware typically requires an active Internet connection to run.
Most adware is safe to use, but some can serve as spyware, gathering information about you from your hard drive, the Web sites you visit, or your keystrokes. Spyware programs can then send the information over the Internet to another computer. So be careful what adware you install on your computer. Make sure it is from a reputable company and read the privacy agreement that comes with it.