According to Maressa Orzack, director of the Computer Addiction Study Center at Harvard University's McLean Hospital, between five and ten percent of Web surfers suffer some form of Web dependency.[10]

Another supporter, David Greenfield, Ph.D. of the Center for Internet Behavior conducted a study with ABC in 1999 and is author of Virtual Addiction. He believes that some services available over the Internet have unique psychological properties which induce dissociation, time distortion, and instant gratifaction, with about 6% of individuals experiencing some significant impact on their lives. However, he says it may not best be seen as an addiction but rather as a compulsion. Greenfield claims that sex, gaming, gambling, and shopping online can produce a mood-altering effect.

According to the Center for Internet Addiction, "Internet addicts suffer from emotional problems such as depression and anxiety-related disorders and often use the fantasy world of the Internet to psychologically escape unpleasant feelings or stressful situations."[11] Over 60% of people seeking treatment for IAD claim involvement with sexual activities online which they consider inappropriate, such as excessive attention to pornography or involvement in explicit sexual conversations online.[12] More than half are also addicted to alcohol, drugs, tobacco, or sex.[11]

"Several counselors and other experts said time spent on the computer was not important in diagnosing an addiction to the Internet. The question, they say, is whether Internet use is causing serious problems, including the loss of a job, marital difficulties, depression, isolation and anxiety, and still the user cannot stop. "The line is drawn with Internet addiction," said Mr. Zehr of Proctor Hospital, "when I'm no longer controlling my Internet use. It's controlling me." Dr. Cash and other therapists say they are seeing a growing number of teenagers and young adults as patients, who grew up spending hours on the computer, playing games and sending instant messages. These patients appear to have significant developmental problems, including attention deficit disorder and a lack of social skills."[13]

In a March 2008 editorial published in the American Journal of Psychiatry, Dr. Jerald Block (2008) argues that Internet Addiction should be included as a disorder in the new fifth edition of the APA's Diagnostic & Statistical Manual [14]. He reasons that symptoms of IA mirror other compulsive/impulsive disorders, including: 1.) excessive use (often associated with a loss of sense of time); 2.) withdrawal symptoms when access is denied; 3.) increasing tolerance (including growing needs for exposure to obtain the same effects); and, 4.) negative repercussions (including social isolation). He notes that research has shown that up to 86% of study subjects showing IA symptoms also exhibited other diagnosable mental health disorders .