Adware is a third party program that displays ads on your computer.  Removing adware is simpler than eliminating malicious spyware.  Adware can be removed by deleting it from your Programs folder.  You can also remove it from the Add/Remove utilities of your computer.  You should also clear your cookies and browsing history to disable the tracking capabilities of adware.  If ads are still appearing on your desktop, you can block the third party site that is communicating with your computer.  You can block it using the Internet security options of your computer.  If these steps are not effective, then you have to install anti spyware program to permanently remove adware from your system.