not sell the virtual currency [@peters2014opening]. For some environments, such as World of Warcraft, the developer Blizzard Entertainment actively monitors and polices the use of their virtual currency to restrict its use within the virtual economy and thus avoid any legal issues that may arise. There are a minority of cases, however, such as Second Life, whose developer Linden Labs does not oppose actively the exchange of the Linden dollar with real fiat currency. This has led to a bi-directional cross over between the virtual currency and real fiat currencies.

Virtual currencies cannot be fully considered as e-money since, as although they share some of its attributes, there is currently no legal founding to enforce the link between fiat physical money and virtual currencies as there is in regulated electronic money transactions. In addition, virtual currencies are not stored in the same unit of account as any fiat currency that would preserve their worth.

Crypto-currencies
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Unlike such virtual currencies which are centrally controlled by a game designer or online platform operator, the development of crypto-currencies has been such that they are typically not operated in a centralized manner. By far the most widely known crypto-currency is Bitcoin, introduced by 