The very concept of legal money has been evolving over the last decades, and particularly in the last years. Scriptural money or “bank money” is now widely considered as an equivalent of paper money and coins, and as such a main part of “sovereign money”. In the last years, new species of “money”, free money and virtual money, have increasingly been accepted as a mean of payment. The common characteristic of these currencies is loss of referral to a central issuing authority directly or indirectly controlled by a sovereign State. However, until very recently free and virtual money have been circulating within small sized communities or among limited online operators. This has changed when a new encryption based virtual money, Bitc...