The Bank of France warned on Thursday about risks related to the digital currency bitcoin, adding its voice to growing concerns about the unregulated, online money. Bitcoin is not backed by any central bank or government, or by physical assets. The Bank of France said the price of bitcoin in legal currencies was inherently volatile and users may find it difficult to convert to real money. The anonymity that bitcoin offer users also raises the risk that they could also be used for money-laundering and financing of terrorism, the central bank said in a publication.