Difficulties in definition of internet addiction phenomenon, its structure, assessment criteria and diagnostics are marked. The necessity to analyze content peculiarities of the Internet activity is emphasized. Leading role of social (in contrast to clinical-psychological and personal) factors in internet-addiction formation (peculiarities of modern way of life, deficit in teachers', parents' and specialists' care) is discussed. Notion "excessive use of the Internet" is introduced; the main signs of which are: cancellation syndrome, loss of control, substitution of reality. The results of the research conducted under "EU Kids online" project and aimed at revealing of psychological factors and popularity of excessive use of the Internet in Russian adolescents It has been stated that excessive use of the Internet is not connected with adolescents' sex and age, has a faint correlation with the frequency and initial age of use, but depend on content of person's activity in the Internet. The latter mediates relationship of parents' strategies with the risk if excessive infatuation for the Internet.