More than $1 billion dollars worth of a digital currency known as "bitcoins" now circulate on the web – an amount that exceeds the value of the entire currency stock of small countries like Liberia (which uses “Liberian dollars”), Bhutan (which uses the “Ngultrum”), and 18 other countries.

So what is a “bitcoin,” and why would anyone use it?

Unlike traditional currency, bitcoins are not issued by a government or even a private company. Instead, the currency is run by computer code that distributes new bitcoins at a set rate to people who devote web servers to keep the code running. The bitcoins are then bought and sold for regular U.S. dollars online.