Digital cryptocurrencies—including bitcoin and litecoin, along with dozens of others—have struggled to win mainstream acceptance in the U.S. Interest in this so-called "Internet money" is not going away, however, which is why regulators are developing rules that that they hope can avert a repeat of last year's Mt. Gox meltdown, when the world's largest bitcoin exchange unexpectedly shut down after losing hundreds of thousands of bitcoins in a cyber attack.
 
The U.S. government has largely sat on the sidelines, leaving states to regulate digital cryptocurrency exchanges. The exchanges, with names such as BitPay and Coinbase, are Web sites for buying, selling and exchanging digital currency. Bitcoin and its ilk are referred to as cryptocurrencies for their use of cryptography to secure transactions and mint new virtual coins.