• What is spyware?
• How did it get on your computer?
• What does it do when it gets there?
• Legality
• Solutions

Some people mistake spyware for a computer virus.

A computer virus is a piece of code designed to replicate itself as many times as possible, spreading from one host computer to any other computers connected to it. It usually has a payload that may damage your personal files or even your operating system.

Spyware, on the other hand, is generally not designed to damage your computer. Spyware is broadly defined as any program that gets into your computer without permission and hides in the background while it makes unwanted changes to your user experience. The damage it does is more a by-product of its main mission, which is to serve you targeted advertisements or make your browser display certain sites or search results.

At present, most spyware targets only the Windows operating system. Some of the more notorious spyware companies include Gator, Bonzi Buddy, 180 Solutions, DirectRevenue, Cydoor, CoolWebSearch, Xupiter, XXXDial and Euniverse.

Here are some of the general ways in which Spyware finds its way into your computer:

• Piggybacked software installation - Some applications -- particularly peer-to-peer file-sharing clients -- will install spyware as a part of their standard install. If you don't read the installation list closely, you might not notice that you're getting more than the file-sharing application you want. This is especially true of the "free" versions that are advertised as an alternative to software you have to buy. There's no such thing as a free lunch.

• Drive-by download - This is when a Web site or pop-up window automatically tries to download and install spyware on your machine. The only warning you might get would be your browser's standard message telling you the name of the software and asking if it's okay to install it.

If your security settings are set low enough, you won't even get the warning.

• Browser add-ons - These are pieces of software that add enhancements to your Web browser, like a toolbar, animated pal or additional search box. Sometimes, these really do what they say they do but also include elements of spyware as part of the deal. Or sometimes they are nothing more than thinly veiled spyware themselves. Particularly nasty add-ons are considered browser hijackers -- these embed themselves deeply in your machine and take quite a bit of work to get rid of. 
  

• Masquerading as anti-spyware - This is one of the cruelest tricks in the book. This type of software convinces you that it's a tool to detect and remove spyware. When you run the tool, it tells you your computer is clean while it installs additional spyware of its own.
  
  

Certain types of spyware can modify your Internet settings so that if you connect through dial-up service, your modem dials out to expensive, pay telephone numbers. Like a bad guest, some spyware changes your firewall settings, inviting in more unwanted pieces of software. There are even some forms that are smart enough to know when you try to remove them in the Windows registry and intercept your attempts to do so.

The point of all this from the spyware makers' perspective is not always clear. One reason it's used is to pad advertisers' Web traffic statistics. If they can force your computer to show you tons of pop-up ads and fake search results, they can claim credit for displaying that ad to you over and over again. And each time you click the ad by accident, they can count that as someone expressing interest in the advertised product.

Another use of spyware is to steal affiliate credits. Major shopping sites like Amazon.com and Ebay.com offer credit to a Web site that successfully directs traffic to their item pages. Certain spyware applications capture your requests to view sites like Amazon and Ebay and then take the credit for sending you there.

Just like anti-spam legislation, these spyware laws can be very difficult to enforce in practice, and the perpetrators know it. It can be tough to find hard evidence connecting individual companies to their spyware products, and, as with all Internet-related lawsuits, there are often battles over which court's jurisdiction applies to the case. Just because it's illegal doesn't mean it's easy to stop.