It's the latest computer security problem to attract the attention of Congress: spyware, or software designed to collect computer users' personal data without their knowledge. Little known a few years ago, spyware is now so common that many educators and other internet users consider it the biggest problem since spam--and now Congress also is investigating.

Secretly piggybacking on downloaded internet software, spyware transmits information about computer usage and generates pop-up advertisements and other annoyances. It often is difficult to uninstall.

Microsoft estimates spyware is responsible for half of all PC crashes and warns that it has become a multimillion-dollar support issue for computer makers, internet service providers, and technicians.

In some cases, it makes a computer unusable.

A research lab in Washington state found one of its computers "hijacked" by pop-up ads, to the point where "we couldn't do anything," said Patrick Clapshaw, the lab's director.

After a week of frustration and several visits by technicians, the problem was eventually solved, but not before causing at least $500 worth of lost data and downtime.

Clapshaw, of Kirkland, Wash., calls spyware worse than spam.

"To me, this is an aggressive computer takeover," he said. "It's the difference between someone dropping fliers on your front porch, or walking around your house following you and annoying you."

Educators, too, report that spyware is a growing problem in their schools. Though commercial software is available that can find and destroy spyware at the desktop level, school leaders contacted by eSchool News say the solutions they've tried so far are inadequate.

"Spyware is probably the biggest problem we face today in our desktop computing environment," said Bob Moore, executive director of IT services for the Blue Valley Unified School District in Overland Park, Kan. "We can deal with viruses, peer-to-peer file swapping software, and other security threats, but we have been unable to find good enterprise spyware solutions."

Ray Yeagley, superintendent of schools in Rochester, N.H., agreed. "Effective filters and anti-spyware applications on our district's computers have helped to reduce the spyware problem, but have not eliminated it," he said. "In addition to being extremely annoying, the popups waste time, which translates into taxpayer dollars."

Members of Congress are taking the threat seriously. At least three bills have been introduced to address the problem, with more likely to follow.

"There is no more pernicious, intrusive activity going on in the internet today" than spyware, said Rep. Joe Barton, R-Texas, chairman of the House Energy and Commerce Committee.

At a hearing April 29 before the panel's subcommittee on commerce, trade, and consumer protection, computer makers and user groups urged Congress to address deceptive behavior, rather than ban categories of software. Citing a new Utah law, the groups said broad legislation could end up prohibiting legitimate practices and stifle innovation.