When the virtual currency bitcoin was released, in January 2009, it appeared to be an interesting way for people to trade among themselves in a secure, low-cost, and private fashion. The Bitcoin network, designed by an unknown programmer with the handle "Satoshi ­Nakamoto," used a decentralized peer-to-peer system to verify transactions, which meant that people could exchange goods and services electronically, and anonymously, without having to rely on third parties like banks. Its medium of exchange, the bitcoin, was an invented currency that people could earn—or, in Bitcoin's jargon, "mine"—by lending their computers' resources to service the needs of the Bitcoin network. Once in existence, bitcoins could also be bought and sold for dollars or other currencies on online exchanges. The network seemed like a potentially useful supplement to existing monetary systems: it let people avoid the fees banks charge and take part in noncash transactions anonymously while still guaranteeing that transactions would be secure.

Yet over the past year and a half Bitcoin has become, for some, much more. Instead of a supplement to the dollar economy, it's been trumpeted as a competitor, and promoters have conjured visions of markets where bitcoins are a dominant medium of exchange. The hyperbole is out of proportion with the more mundane reality. Tens of thousands of bitcoins are traded each day (some for goods and services, others in exchange for other currencies), and several hundred businesses, mostly in the digital world, now take bitcoins as payment. That's good for a new monetary system, but it's not disruptive growth. Still, the excitement is perhaps predictable. Setting aside Bitcoin's cool factor—it might just as well have leapt off the pages of Neal ­Stephenson's cult science-fiction novel Snow Crash—a peer-to-peer electronic currency uncontrolled by central bankers or politicians is a perfect object for the anxieties and enthusiasms of those frightened by the threats of inflation and currency debasement, concerned about state power and the surveillance state, and fascinated with the possibilities created by distributed, decentralized systems.