Spyware is software designed to collect information about you for a variety of purposes, including advertising, credit card fraud, and identity theft. The information is gathered in a number of ways, such as by recording the keys that you type, recording your Web browsing history, and even scanning documents you have saved on your hard drive.

Although collecting your information for advertising is generally just annoying, it can be harmful to your computer since it uses up resources. When your computer is infected with spyware, you might notice a significant slowing in performance and your computer will just generally react sluggishly to your commands. And, if too much spyware builds up, your computer might crash or fail to start up.

Spyware used to collect your financial information is a much more serious problem. Some types of spyware attempt to record your password as you log into certain websites, such as your bank's site or your credit card company's site. Or, they might try to capture your credit card number as you enter it during an online shopping checkout.

Spyware doesn't spread like a virus or a worm; your infected computer won't try to spread its disease to others. Spyware gets into your system by tricking you or by working its way through some of the less secure spots on your computer. In most cases, you'll never see it happening. A lot of spyware is transmitted as a Trojan horse, where it masquerades as something useful-sometimes even as security software!

Spyware sometimes comes bundled with software that you can download from the Internet, such as certain shareware programs. When you download the program you want, the unwanted spyware is downloaded as well.

Still other spyware targets holes in your Web browser or in software on your computer. This happens when you visit a website containing spyware code that attacks your browser and installs the spyware. This is often referred to as a "drive-by download."

Unfortunately, once one spyware program gets in, your computer becomes more vulnerable to additional spyware. Many users assume the significant decrease in efficiency is a hardware program, and might go so far as to purchase a new computer. When a computer is extremely infected, you might actually have to back up your files and perform a clean reinstallation of all the software on your computer. This is a time-consuming process and requires you to set up your computer preferences as though you were setting up your computer for the first time.

The best thing you can do to protect yourself from spyware is to purchase an anti-spyware program. These programs work to fight spyware by preventing its installation and by detecting and disabling existing spyware. Some spyware programs don't perform both of these functions.

If you purchase a program that detects and disables existing spyware, be sure to schedule it to run on a regular basis. When you run a program of this type, it will scan your Windows registry, operating system files, and all installed programs. You'll then see a list of potential threats from which you can decide which to delete and which to keep.

The bad news is that some fake anti-spyware programs have appeared on the market. In addition, you might see ads on your computer that appear to be pop-ups generated by your computer system indicating you have a spyware infection. When you click on these pop-ups, you'll be directed to a site that instructs you to buy certain programs.

To avoid being taken in by these malicious programmers, do your homework. Only buy an anti-spyware program from a reputable dealer. Before buying, do some research into the program and look for customer reviews. Although spyware is extremely common on the Internet, you can keep those spies out of your computer and your home.