Spyware

Programs classified as spyware send information about you and your computer to somebody else. Some spyware simply relays the addresses of sites you visit or terms you search for to a server somewhere. Others may send back information you type into forms in Internet Explorer or the names of files you download. Still others search your hard drive and report back what programs you have installed, contents of your e-mail client's address book (usually to be sold to spammers), or any other information about or on your computer – things such as your name, browser history, login names and passwords, credit card numbers, and your phone number and address.

Spyware often works in conjunction with toolbars. It may also use a program that is always running in the background to collect data, or it may integrate itself into Internet Explorer, allowing it to run undetected whenever Internet Explorer is open.arstechnica