DENVER -- Pop-up ads aren't just annoying, they're now taking on the sneaky task of following your every move.

Lillian and Christine Mallia have found something they didn't know was on their computer. It's the culprit behind all the pop-up ads.

When they log on to the Internet, there are pop-up ads everywhere and a homepage that mysteriously changes.

"I logged on and it was something totally different," said mother Lillian Mallia.

How'd it happen?

Spyware, also known as adware, could be hiding in music or programs you download from the Internet. Spyware changes your computer settings, adding links to advertisers' sites and quietly sharing every move you make on the Web with advertisers.

"These adware components have the capability to monitor a computer user's every key stroke command," said Debbie St. Clair, of UnwantedLinks.com.

UnwantedLinks.com is a site devoted to fighting spyware. The site's creator said after spyware sneaks in, it often displays a licensing statement you usually ignore, but don't.

One warning clearly states that it will collect which Web pages you view, what software is on your computer and make a note of your name and zip code. Sometimes, you don't even get this much warning.

"Some of these things can be picked up just viewing a Web site," St. Clair said.

A computer professional for social responsibility has a special name for this type of advertising -- sleezeware.

"In fact, sleezeware does not break any laws," said computer specialist Coralee Whitcomb.

The good news is there's software to fight sleezeware like the 130 spyware files on Lillian and Christine's computer.

"I think that's very underhanded and devious," said Lillian Mallia said.

If you instant message or download music programs, chances are you have spyware on your computer. One way to know is if your computer seems to have slowed down; The spyware may be consuming your computer's resources.

For more information check out Computer Professionals for Social Responisbility or UnwantedLinks.com.