What is spyware?

 David Eckstein turned on his computer one day and launched his Web browser, just as he had every day. This time, however, CNN.com did not automatically open. Instead, the page was a search engine he'd never heard of.

Eckstein tried changing the browser settings back to CNN but the search engine would return whenever he rebooted. Finally, he just gave up.

The San Francisco marketing consultant is yet another victim of spyware, an amorphous class of software that mostly gets onto people's computers without their knowledge. So resource-hungry, it often renders the machines unusable.

"It makes you want to throw your computer out the window," Eckstein said.

In the past year, the problem has become epidemic as people spend more time online and spyware developers get more aggressive.

"It makes spam look like a walk in the park," said Bob Bowman, chief executive of Major League Baseball's Internet unit, which in June started banning new advertisers from using such techniques.

As part of a government-backed study, technicians visited Jenna Dye recently in Young Harris, Georgia, and found 1,300 spyware-related items on her machine.

"It would shut itself down in the middle of doing stuff. We had lots of pop-ups. The (CD-ROM) drawers would pop open," the mother of two complained. "It's frustrating. We spent $1,800 on our computer and we didn't want to use it."

Until the machine was cleaned up, Dye and her husband would make 2 1/2 hour trips to the nearest mall to avoid shopping online. "We use it every day now again," she said.

Spyware was found on the computers of 80 percent of participants in the study, conducted by America Online Inc. and the National Cyber Security Alliance.