Bitcoin is the first, and the biggest, "Cryptocurrency" - a decentralised tradable digital asset.
Bitcoin can only be used as a medium of exchange and in practice has been far more important for the dark economy than it has for most legitimate uses.
Neil Wilson, senior market analyst at ETX Capital, said: "The legitimacy this gives bitcoin as a tradeable asset is very important. The market cap of bitcoin now exceeds that of IBM, Disney [or] McDonald's."
Warning of looming pain for bitcoin buyers, Wilson added: "But for traditionalists, it's hard to fathom. Rather than a commodity or currency, bitcoin is like owning stock in a company that will only ever issue 21m shares and never pay a penny in dividends. The only way it has value is if the next guy is willing to pay you more for it - the greater fool. With no intrinsic value to bitcoin, it's hard to see this as anything other than a giant speculative bubble."
Bitcoin is a virtual currency that emerged in the aftermath of the financial crisis.
Source: The Guardian