What you don't know can hurt you.

• Position: TRENDS AND TRANSITIONS

Four out of five computer users have spyware or adware programs on their computer but don't know it.

These programs might cause pop-up ads to appear, sometimes relentlessly; others might change a computer user's home page, add links to his list of favorites sites, or redirect search requests to a Web site of the spyware company's choosing. Spyware and adware also can slow a computer's operations or cause it to malfunction or crash. More sinister types of spyware, such as keystroke loggers, can capture everything a person types, including passwords, financial information, and the contents of e-mail messages. Some of these programs even claim to detect and remove spyware, but instead do nothing or actually install spyware.

In a short time, spyware has gone from being a minor annoyance to a major problem, leading state lawmakers in more than half the states this year to consider ways to help curb the problem. So far this year, Arizona, Arkansas and Virginia passed laws and bills have gone to the governor in three more states.

Utah and California in 2004 enacted anti-spyware legislation. Utah's law faced a court challenge on grounds that it violated free speech rights and hindered interstate commerce. Legislation amending the law passed this year. According to the law's sponsor, Senator Steven Urquhart, this year's bill more narrowly addresses the problem.

California's...