Children with ADHD have difficulty focusing, which leads to problems in school. Their impulsivity makes them more likely to be in car accidents. They are also more likely to use alcohol or marijuana daily. Because children with ADHD crave novelty, it makes sense that the Internet would appeal to them, Koplewicz said.
"Parents of children who have these disorders, most specifically ADHD, should be most vigilant and cautious about the added risk the Internet holds for their children compared to the rest of the population," Koplewicz said.
Also, pediatricians and mental health professionals should ask their teenage patients about their Internet usage, Koplewicz added.
Even with those steps, in a society in which the Internet is increasingly used for schoolwork, employment, socializing and communicating, curtailing computer use is difficult.
"Everyday, the Internet becomes more integral to life," Gilbert said. "It's a tough new problem for psychologists and parents because they can't get away from it. The Internet will be at every table, in every bar, classroom and maybe on their wrist."
Gilbert advised parents to focus on helping their child deal with their depression, hostility or social phobia.
"It has to be dealt with at the source. It's not about taking their Internet away," Gilbert said. "They are going to be confronted with that media wherever they go."
The National Institute on Media and the Family has more on Internet addiction.
SOURCES: Michael Gilbert, senior fellow, Center for the Digital Future, University of Southern California's Annenberg School for Communication, and author, "The Disposable Male"; Harold Koplewicz, M.D., director, New York University Child Study Center and chair, department of child and adolescent psychiatry, New York University Langone Medical Center; October 2009 Archives of Pediatrics & Adolescent Medicine