In May 2005, the privacy software company Webroot revealed a startling statistic: At any given time, said the company's State of Spyware Report, two of every three personal computers in the United States are infected with spyware that raises your risk of identity theft.

When it comes to identity theft, fraud expert Sid Kirchheimer says the primary purpose of spyware is to capture sensitive online data: user names, passwords and account numbers.

How does spyware infiltrate your computer? It can piggyback on other applications, hiding inside the "install" commands of Internet software, such as music download programs.

How to Protect Yourself
The first rule of preventing spyware is to be careful about what you download on your computer, says Doug Tygar, Phd, a computer science professor at the University of California, Berkeley. Think twice about installing freebie software, no matter how enticing it appears. Forbidden landing zones should include any website offering sexy photos of your favorite starlet. And never open unsolicited e-mails promising discount products.

The second rule is to scan your computer once a week or more with a good anti-spyware program. "My recommendation is to use Ad-Aware," suggests Dr. Tygar. "It's freeā€”and, based on my experience, it's among the best anti-spyware programs available." For a free Ad-Aware download, visit