Video: Five reasons why Bitcoin is the most dangerous currency in the world Coins can only be accessed, or "mined" by solving complex computing problems. As each block of coins gets mined, the problems become harder and harder, requiring increased computing grunt. This limits the supply of the coins. Bitcoin is the world's first decentralised currency, which means it isn't controlled by any government or bank. This has its advantages: you can transfer Bitcoins tax-free, and transactions are usually free, or relatively low cost. But Bitcoins are also wildly volatile. In January 2013, one Bitcoin was valued at around $14. In November 2013, that value peaked at $1,124 but plummeted to $539 the following month. This currency is private and totally anonymous, which has prompted a surge in users choosing Bitcoins to pay for illegal goods, primarily through the online darknet marketplace Silk Road. The popularity of Bitcoin has opened the door for several other cryptocurrencies. Litecoin, Dogecoin, Peercoin, Quarkcoin have all sprung up in recent years.