How do you know you're addicted? Read the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition -- at least that's what he did. In short, three of the following seven criteria must apply (edited for brevity):
He then used a few questions from the Internet Addiction Tendency Scale (Song et al., 2002) to find addicted users. He also created a few new questions for a Custom Habit Scale to find habitual users amongst the non-addicted ones. He also used Short Imaginal Processes Inventory based on studies done on TV addiction to investigate positive constructive daydreaming, guilt and fear of failure daydreaming, and poor attentional control.
The main result is that addicted users turn to the Internet in order to distract themselves away from excess negative thoughts and unstructured time.
(From AlexSchroeder's homepage )