University of Leeds psychologists found evidence that some users have developed a compulsive Internet habit, whereby they replace real-life social interaction with online chat rooms and social networking sites.

"The Internet now plays a huge part in modern life, but its benefits are accompanied by a darker side," Dr. Catriona Morrison of the University of Leeds, the study's lead author, said in a statement.

"While many of us use the Internet to pay bills, shop and send e-mails , there is a small subset of the population who find it hard to control how much time they spend online, to the point where it interferes with their daily activities."

These "Internet addicts" spent proportionately more time browsing sexually gratifying Web sites, online gaming sites and online communities and had a higher incidence of moderate to severe depression than non-addicted users.

"Our research indicates that excessive Internet use is associated with depression, but what we don't know is which comes first -- are depressed people drawn to the Internet or does the Internet cause depression?" Morrison asked.

The study is published in Psychopathology.