Beware the spy on your hard drive.(Have You Heard?)

I'm competent, but not a whiz, on computers. So when the team working on the Internet security article for this issue of CONSUMER REPORTS sat me down to explain "adware"--spyware that throws advertisements onto your computer screen--they started with the basics.

"Imagine you stop at the newsstand to buy a New York Times," one of the reporters said. "As you carry it to the counter, a stranger shoves a Daily News in your hand and shouts, 'Read this instead.' Then he tags along everywhere you go, popping up at inopportune times, dragging on your sleeve, and slowing your work down to a crawl." You may lose data or, in some cases, your whole computer.

That's pretty much how the most insidious adware works. It sits, sometimes undetectably, on your computer, watching where you go on the Internet and feeding you ads based on what you do in cyberspace. When you show an interest in booking a flight on a particular airline, say, or buying a cell phone from one company, it blasts you with ads for the airline's or cell phone company's competitors, sometimes blanketing your screen with interlopers' offerings. And it makes your computer run ... oh ... so ... slowly.

How did spyware get onto your hard drive? At some point, when you downloaded free software, a screensaver, or a game, it came along for a ride, with or without your permission. Of course, you didn't know you gave permission. That little detail may have been buried in the legalese in the end-user ...