Adware

Adware is also known as malware, sneakware, or spyware. Adware is a type of software program that’s installed without a users consent or knowledge while another program is being installed on the computer. Much like spyware an adware program is used to track an individuals Internet activities and/or habits to help companies advertise more efficiently.
Adware is commonly installed on a computer with free programs to help support the development of that program. Like spyware adware can be located and removed from a computer using software utilities available on the Internet.

Adware means a program that displays advertisements on your computer. Not the usual advertisements you see on web pages that you visit: adware pop-up advertising windows (or in some cases, say some voice message) on your system are not generated by the websites you happen to visit. Dialers are programs that get installed on your system and try to dial up to some telephone line somewhere, sometimes incurring you expensive phone bills. Keyloggers record the keystrokes you type on your computer (some are more sophisticated in capturing screen shots, etc), and either log them or report them to the person who installed them.