What is spyware? And what harm can it do to my network?

Even in its most innocuous form, spyware is an invasion of privacy.

Spyware programs such as Cydoor, Gator, Lop.com and Xupiter install without the user's knowledge by piggybacking on peer-to-peer file-sharing programs, cute executable images or a long list of freeware.

Primarily used for target advertising purposes, spyware tracks a user's Web habits. Some programs log keystrokes and even capture and transmit screen images.

"These programs are hard to avoid because they come bundled with other things, and it's not always apparent when they're installing themselves. And once they're on computers, they can be difficult, time-consuming and costly to remove," says Michael Steffen, policy analyst with the Center for Democracy and Technology (CDT) in Washington, D.C.

At its worst, spyware becomes a dangerous tool in the hands of the wrong people.

"Today, spyware's annoying but relatively benign. But Gartner believes spyware will get more malicious in the future and be used for password harvesting, credit card number theft and other forms of identity theft," says John Pescatore, a Gartner analyst. Mark Maiffret, chief hacking officer for eEye Digital Security, sees even more sinister uses for spyware, such as capturing and transmitting Microsoft Word and Excel documents to steal corporate secrets.

This is not to mention the unprotected tunnels being opened to the desktops by unknown programs that aren't coded with security in mind, adds Jeff Horne, researcher for Internet Security Systems, which makes RealSecure intrusion-detection software.

How to avoid spyware

Enforcing employee Internet use policy is your first line of defense, Maiffret says. His advice is:

•  Configure desktop browsers and Outlook using Microsoft Domain Security Policies.

•  Block ActiveX and other executables.

•  Manage scripting.

•  Filter Web content through an HTTP proxy.

•  If necessary, segment certain employees from using the Internet if they don't need it to do their jobs.

Employees also should be taught how to surf the Web safely, says Ian Poynter, chief security officer for Bit9, a security software start-up. Keep user education simple, he says, by sticking to the following points: