Bitcoins are a currency controlled by no government, no company, and no group, but rather by maths: a series of complex cryptographic calculations rule how many Bitcoins are in existence and how many are traded.
Worth more than £500m, it’s the world’s fastest growing.
Silk Road is probably the biggest use of the currency, followed by an unregulated online gambling site known as Satoshidice.
But more mainstream services are adopting the currency: the blogging platform WordPress accepts Bitcoins, as does the social news site Reddit. WikiLeaks opened up to Bitcoin when the mainstream banking system blockaded the site.
The people behind Bitcoin speak to the Guardian’s James Ball at their home in a squat in central London.