**2.1. Definition of Internet addiction**

There are many definitions of Internet addiction. Some authors defined it as "excessive Internet usage" [7, 8], "problematic Internet use" [9], "Internet dependency" [10], or "pathological Internet usage" [11]. This variation is related to lack of agreement in definitions among studies that investigated the different symptoms and characteristics of IA. Young [7] developed definition for Internet addiction, which was "maladaptive pattern of Internet use that lead to clinically significant impairment or distress".

It was also defined as "a psychological dependence on the Internet, despite the purpose once logged on" [12]. In his second definition that based on the Diagnostic and Statistical Manual IV (DSM-IV) pathological gambling diagnosis criteria to Internet use, Young [13] defined Internet addiction as an impulse-control disorder and made a definition that consists of eight criteria and requires the fulfillment of five out of eight for the identification of an individual to be addicted. This criteria are (1) excessive mental effort with the Internet, (2) the need for longer time online, (3) repeated attempts to decrease Internet use, (4) withdrawal symptoms when decreasing Internet use, (5) issues in time management, (6) environmental distress (family, friends, school, and work), (7) lying about time spent online, and (8) mood modification through Internet use. Goldberg [14] defined Internet addiction on the basis of the DSM-IV substance addiction criteria as a behavioral addiction functions as a coping mechanism.

Later on, Block [15] defined it as "compulsive behaviors related to any online activities that influence normal activity daily living and lead to stress on social and family relationships, lying, poor achievement, and fatigue". Other researchers conceptualized it as "an impulse control disorder where individuals loss ability to control Internet use" [16, 17].
