Bitcoin is the most popular example out of some 67 virtual currencies, that have a combined value of about $13bn (€9.4bn, £7.9bn), according to a website that ranks virtual currencies.
According to coinmarketcap.com, which currently lists 67 "cryptocurrencies", the total market value of all virtual currencies is $12.94bn as at 30 December. With a supply of more than 12 million, bitcoins are currently worth $9.1bn at $750.99 per coin.
Out of the 67 currencies, there are at least 14 currencies including bitcoin that are valued at more than $1, according to the website.
Ripple, a distributed, peer-to-peer payment system, has the second-largest market capitalisation, according to coinmarketcap.com.
Litecoin, which is often accepted by retailers that take bitcoin, crossed $1 a few months ago and is currently valued at $23.99. Litecoin has a market cap of $585m at present, the third largest market capitalisation among virtual currencies.
MasterCoin and Peercoin are the virtual currencies with the fourth and fifth largest market capitalisations at $103m and $91m, respectively.
Virtual currencies that have a value of more than $1 include Namecoin, ProtoShares, Primecoin, Novacoin, Anoncoin, Cryptogenic Bullion, Tickets, Unobtanium, Diamond, BitBar, Franko and Elacoin.
A virtual currency is a form of unregulated digital money, which can be used as an alternative to current payment methods. A growing number of retailers, restaurants and entertainment venues are accepting virtual currencies to pay for goods and services. These currencies are not issued or guaranteed by a central bank.
The currency's growing popularity has also raised concerns. Critics say virtual currencies could be used for drug transactions, money-laundering and other illegal activities due to the near anonymity of those who deal in them.
Countries like China and India have banned bitcoin exchanges operating there.
Top 10 Virtual Currencies by Market Cap
|Rank||Name||Market Cap||Price||Total Supply|
|3||Litecoin||$ 585,305,729||$23.99||24,401,342 LTC|