Are you being watched?

If your computer starts to behave strangely or displays any of the symptoms listed below, you may have spyware or other unwanted software installed on your computer.

I see pop-up advertisements all the time
Some unwanted software will bombard you with pop-up ads that aren’t related to a particular website you’re visiting. These ads are often for adult or other websites you may find objectionable. If you see pop-up ads as soon as you turn on your computer or when you’re not even browsing the web, you may have spyware or other unwanted software on your computer.

My settings have changed and I can’t change them back to the way they were
Some unwanted software has the ability to change your home page or search page settings. This means that the page that opens first when you start your Internet browser or the page that appears when you select "search" may be pages that you do not recognize. Even if you know how to adjust these settings, you may find that they revert back every time you restart your computer.

My web browser contains additional components that I don’t remember downloading
Spyware and other unwanted software can add additional toolbars to your web browser that you don’t want or need. Even if you know how to remove these toolbars, they may return each time you restart your computer.

My computer seems sluggish
Spyware and other unwanted software are not necessarily designed to be efficient. The resources these programs use to track your activities and deliver advertisements can slow down your computer and errors in the software can make your computer crash. If you notice a sudden increase in the number of times a certain program crashes, or if your computer is slower than normal at performing routine tasks, you may have spyware or other unwanted software on your machine.

 http://www.microsoft.com/windows/products/winfamily/defender/default.mspx

Spyware is a general term used to describe software that performs certain behaviors such as advertising, collecting personal information, or changing the configuration of your computer, generally without appropriately obtaining your consent first.

Spyware is often associated with software that displays advertisements (called adware) or software that tracks personal or sensitive information. Not all software that provides ads or tracks your online activities is bad. For example, you might sign up for a free music service, but you "pay" for the service by agreeing to receive targeted ads. If you understand the terms and agree to them, you may have decided that it is a fair tradeoff. You might also agree to let the company track your online activities to determine which ads to show you.

Other kinds of spyware make changes to your computer that can be annoying and can cause your computer to slow down or stop responding. These programs can change your web browser’s home page or search page, or add additional components to your browser you don’t need or want. These programs also make it difficult for you to change your settings back to the way you originally had them.

There are a number of ways spyware or other unwanted software can get on your computer. A common trick is to covertly install the software during the installation of other software you want such as a music or video file sharing program. The key in all cases is whether or not you (or someone who uses your computer) understand what the software will do and have agreed to install the software on your computer.

Whenever you install something on your computer, make sure you carefully read all disclosures, including the license agreement and privacy statement. Sometimes the inclusion of unwanted software in a given software installation is documented, but it might appear at the end of a license agreement or privacy statement.

http://www.microsoft.com/windows/products/winfamily/defender/default.mspx