(NEW YORK, NY) –– At least 200,000 Internet users are hooked on porn sites, X-rated chat rooms or other sexual materials online, researchers say in one of the first studies to estimate the number of "cybersex compulsives."

"This is a hidden public health hazard exploding, in part, because very few are recognizing it as such or taking it seriously," the researchers said.

The study, conducted by psychologists at Stanford and Duquesne universities, appears in the March issue of the journal Sexual Addiction and Compulsivity.

The researchers classified users as "cybersex compulsives" if they spent more than 11 hours a week visiting sexually oriented areas and scored high on a 10-item questionnaire about relationships and attitudes toward sex.

The study was led by Al Cooper, clinical director at the San Jose Marital and Sexuality Centre and Stanford's training coordinator for counseling and psychological services.

The researchers found evidence that compulsives have more problems with relationships and jobs than Internet users who visit X-rated sites casually.

Past studies examined how many people visited porn sites and how much time they spend there. But very few studies attempted to estimate the number of compulsives, said Mark Wiederhold, a professor at the California School of Professional Psychology in San Diego.

He called the conclusions conservative, but significant, "pointing to a huge number we can't ignore."

Wiederhold and Cooper raised caution about how participants were picked. For the survey, conducted in the spring of 1998, more than 13,500 visitors to the MSNBC news site were asked to answer a questionnaire. Because of such self-selection, it is impossible to tell whether the group accurately represents all Internet users.

Plus, participants may have lied or denied they had a problem.

The researchers tossed out incomplete responses or multiple questionnaires that appeared to come from the same individual. They kept 9,265 surveys from respondents ages 18 to 90.

Only 96 of these people, or about 1 percent, fit researchers' definition for being cybersex compulsive. Applying that percentage to 20 million people visiting sexual sites each month, the researchers came up with the figure of 200,000.