It sits in memory, watching everything the computer does--the websites it displays, the passwords used to get into them, the advertisements that get clicked on. This program silently and secretly gathers all of this information, without the user's knowledge. Then, at some point, it connects to a server somewhere on the Internet, and hands over this collection--again, without letting the owner of the computer know what it's done.

Scary thought?

Experts believe that at least six out of ten--perhaps as many as nine out of ten--computers on the Internet have this kind of malware installed. Like a virus, many spyware programs run without the user's consent or knowledge.

There is an entire industry devoted to gathering demographics information through the use of spyware, and there is another industry that's grown to combat spyware.

Spyware is meant to capture "demographics." This is meant to help advertisers better target their ads. For example, if a piece of spyware reports that the user recently visited websites for car dealerships, then the spyware server would then send ads for cars to the computer.

Many people, however, regard this as an invasion of privacy. Spyware companies claim to only gather "generic" information, like web site addresses and zip codes, but it's still very easy to gather critical information. Anything entered into a web form can end up in the spyware collection--such things as phone numbers, email addresses, credit card numbers, and even social security numbers can all find their way into a spyware database.

In the end, it comes down to personal preference. Some popular programs have spyware attached, and will quit working if the spyware is uninstalled--so the user has to decide whether that program is worth it.

Provided, of course, the user even knows that the spyware is running on his system.