Online role-playing games (MMORPGS) have led the field in terms of the length and depth of gameplay offered. Characters develop, or level up, in accordance with the amount of time spent playing, the quests achieved, and the number and type of opponents killed. Trading plays an important role in getting in-game objects. In-game currency (usually virtual gold) is an object in itself. With World of Warcraft, the most popular MMORPG ever, resourceful players realized right from the start that they could supplement their real-world income.”]
Source: https://securelist.com/online-gaming-fraud-the-evolution-of-the-underground-economy/36320/