The system is peer-to-peer; users can transact directly without needing an intermediary. Transactions are verified by network nodes and recorded in a public distributed ledger called the blockchain. The ledger uses bitcoin as its unit of account. The system works without a central repository or single administrator, which has led the U.S. Treasury to categorize bitcoin as a decentralized virtual currency.
Bitcoin is often called the first cryptocurrency, although prior systems existed. Bitcoin is more correctly described as the first decentralized digital currency. It is the largest of its kind in terms of total market value.
Bitcoins are created as a reward for payment processing work in which users offer their computing power to verify and record payments into a public ledger. This activity is called mining and the miners are rewarded with transaction fees and newly created bitcoins. Besides being obtained by mining, bitcoins can be obtained in exchange for different currencies, products, and services. Users can send and receive bitcoins for an optional transaction fee.
Bitcoin as a form of payment for products and services has grown, and merchants have an incentive to accept it because fees are lower than the 2–3% typically imposed by credit card processors. Unlike credit cards, any fees are paid by the purchaser, not the vendor. The European Banking Authority and other sources have warned that bitcoin users are not protected by refund rights or chargebacks. Despite a big increase in the number of merchants accepting bitcoin, the cryptocurrency does not have much momentum in retail transactions.
The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and media. Criminal activities are primarily centered around black markets and theft, though officials in countries such as the United States also recognize that bitcoin can provide legitimate financial services. Bitcoin has drawn the support of a few politicians, notably U.S. Presidential candidate Rand Paul, who accepts donations in bitcoin.