The nationwide study suggests that more than one in eight adults has a hard time staying away from the Internet for more than a few days at a time. And one in 11 tries to hide his or her online habit.

"We often focus on how wonderful the Internet is -- how simple and efficient it can make things," said Elias Aboujaoude, the study's author. "But we need to consider the fact that it creates real problems for a subset of people."

The survey, conducted over the phone, found that nearly 70 percent of respondents were regular Internet users and 14 percent found it hard to stay offline for several days at a time.

Online Junkies

Aboujaoude, a clinical assistant professor in psychiatry and behavioral sciences and director of Stanford's Impulse Control Disorders Clinic, said that more and more Internet users are visiting their doctors for help with addictions to cyberspace.

"In a sense, they're using the Internet to self-medicate," Aboujaoude said. "And obviously something is wrong when people go out of their way to hide their Internet activity."

Among the habits online users develop is strong compulsion to check e-mail, post blog entries, or visit Web sites or chat rooms. "It is not unlike what sufferers of substance abuse or impulse-control disorders experience," said Aboujaoude, noting the similar repetitive, intrusive, and irresistible urge to perform an act that might be pleasurable in the moment but that can lead to significant problems on the personal and professional levels.

Internet Issues

"We need to consider the fact that it creates real problems for a subset of people," he said.

The study found approximately 12 percent of Internet users often stay online longer than intended, more than 12 percent said they saw a need to cut back on their Internet use, and 8.7 percent tried to conceal "nonessential" Internet use from family, friends, and employers.

According to the research, the typical Internet-addicted user is a single, college-educated, white male in his 30s who spends approximately 30 hours a week on nonessential computer use.

Not surprisingly, said Aboujaoude, online pornography and online gambling are big issues when it comes to Internet addiction. Users also reported relying on the Internet to escape problems or a bad mood, and said their relationships have suffered because of excessive Net use.

However, Aboujaoude also said it is too soon to give the excessive user a clinical diagnosis.

"We're not saying this is a diagnosis -- we still need to learn a lot more," he said. "But this study was a necessary first step toward possibly identifying something clinically significant."