The term adware refers to any software which displays ads, whether or not it does so with the your consent. Programs such as the Eudora mail client display advertisements as an alternative to shareware registration fees. These classify as "adware" in the sense of advertising-supported software, but not as spyware. They do not operate surreptitiously or mislead the user.
Many of the programs classified as spyware function as adware in a different sense: their chief behavior consists of displaying advertising. Gator Software is an example of this type of program. Web sites frequently install Gator on client machines in a sneaky manner, and it makes money for the installing site by displaying ads to the user. The user ends up with a large number of pop-up.
Other spyware programs report what websites the user visits, and aid in the display of ads. Monitoring web activity (and sending it to whatever company put the spyware there in the first place) builds a marketing profile on users in order to deliver "targeted" ads. When a large number of pieces of spyware have infected a Windows computer, the way to fix your computer may involve backing up user data, and fully reinstalling the operating system.
There are many programs out there to find and remove spyware . These include programs designed to remove or to block spyware. I suggest installing at least two different anti-spyware programs as these programs tend to have about a 75% success rate. By using more than one program you increase your odds of keeping your system clean. There are several fake anti-spyware programs out there so be careful what you use. I'd suggest Windows Defender, Adaware, and Spybot Search and Destroy.
There are also some things you can do to avoid spyware, such as using a web browser other than Internet Explorer. I suggest either Firefox or Opera. Both are free and are much safer than Internet Explorer. No browser is completely safe.
Be careful what you install on your computer. Certain shareware programs offered for download contain spyware. one thing you can do is only get programs from a reputable source, such as Cleansoftware.org, which offers only software that has been verified to not contain spyware. Another way to protect yourself is to actually READ what the installer is saying instead of just clicking next. A lot of times the installer tells you it's going to install bundled software with the program you are trying to install.
Hopefully this will be enough to keep your online experience free of spyware.