It's sometimes called the "new spam." It slips right through firewalls and antivirus programs, riding the coattails of legitimate programs you've chosen to download from the Internet. In its more common and benign forms, it will send you pop-up ads targeted to your interests and clog your computer's memory. At its most malicious, it can steal your passwords and credit-card numbers, maybe even let a remote user take over your computer.
It's spyware, a broad term for programs that hide on users' computers without their knowledge. It has become so pervasive that both federal and state governments are looking into ways to prevent or at least regulate it.
While it's hard to tell the share of computers that have been infected with spyware, estimates run as high as 95 percent. One popular spyware detection program, Spybot Search and Destroy, lists nearly 800 spyware programs that it can find and remove.
While most of the spyware found on computers appears relatively benign so far, experts suggest users take measures to protect themselves (see list page 17).
Children online can be especially vulnerable because they may have less technical savvy and frequently download so-called peer-to-peer software from the Internet, often called freeware or shareware.
"One of the ways these programs end up on people's computers is that they can be bundled with other free applications they download, which can include file-sharing applications, screen savers, or other kinds of free utilities," says Michael Steffen, a policy analyst at the Center for Democracy and Technology (CDT) in Washington, D.C.
Kazaa, a widely used music- swapping program that has been downloaded 270 million times, has carried at least 12 kinds of hidden spyware at various times over the past two years, according to a recent study at the University of Washington in Seattle.
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