Those addicted to the Internet show differences in their brains from those who are not addicted. MRI scans of those classified as addicted show damage to both the white matter and fibers that may damage cognitive functions.
However the study of 17 adolescents by Chinese researchers with 16 controls is relatively small. The resulting cognitive impairment is similar to that observed in alcoholics and compulsive gamblers.
Internet addiction is not officially recognized by health care authorities. However there are individuals who appear to feel a compulsion to be on line. The desire is compelling enough to interfere with their everyday life. If forced to stay off line such individuals show withdrawal symptoms. Certainly such behavior is very much like that of an addict. We all probably know such people as well. Perhaps even some bloggers suffer from the addiction. For much more see this CBC article