In 2012, the Cryptocurrency Legal Advocacy Group (CLAG) stressed the importance for taxpayers to determine whether taxes are due on a bitcoin-related transaction based on whether one has experienced a "realization event": when a taxpayer has provided a service in exchange for bitcoins, a realization event has probably occurred and any gain or loss would likely be calculated using fair market values for the service provided."
On 3 March 2014, Flexcoin announced it was closing its doors because of a hack attack that took place the day before. In a statement that once occupied their homepage, they announced on 3 March 2014 that "As Flexcoin does not have the resources, assets, or otherwise to come back from this loss [the hack], we are closing our doors immediately." Users can no longer log into the site.
In July 2013, a project began in Kenya linking bitcoin with M-Pesa, a popular mobile payments system, in an experiment designed to spur innovative payments in Africa. During the same month the Foreign Exchange Administration and Policy Department in Thailand stated that bitcoin lacks any legal framework and would therefore be illegal, which effectively banned trading on bitcoin exchanges in the country. According to Vitalik Buterin, a writer for Bitcoin Magazine, "bitcoin's fate in Thailand may give the electronic currency more credibility in some circles", but he was concerned it didn't bode well for bitcoin in China.
The overwhelming majority of bitcoin transactions take place on a cryptocurrency exchange, rather than being used in transactions with merchants. Delays processing payments through the blockchain of about ten minutes make bitcoin use very difficult in a retail setting. Prices are not usually quoted in units of bitcoin and many trades involve one, or sometimes two, conversions into conventional currencies. Merchants that do accept bitcoin payments may use payment service providers to perform the conversions.
Mining is a record-keeping service done through the use of computer processing power.[e] Miners keep the blockchain consistent, complete, and unalterable by repeatedly grouping newly broadcast transactions into a block, which is then broadcast to the network and verified by recipient nodes. Each block contains a SHA-256 cryptographic hash of the previous block, thus linking it to the previous block and giving the blockchain its name.:ch. 7
It's impossible to say how much bitcoin has increased in price single its earliest incarnation, because its value back then was in the fractions of cents. A conservative estimate, based on bitcoin's current price being around $6,300 per coin, and its early price being less than $0.01, would see bitcoin's value increasing more than 1 million fold in the last decade.
In the blockchain, bitcoins are registered to bitcoin addresses. Creating a bitcoin address requires nothing more than picking a random valid private key and computing the corresponding bitcoin address. This computation can be done in a split second. But the reverse, computing the private key of a given bitcoin address, is mathematically unfeasible. Users can tell others or make public a bitcoin address without compromising its corresponding private key. Moreover, the number of valid private keys is so vast that it is extremely unlikely someone will compute a key-pair that is already in use and has funds. The vast number of valid private keys makes it unfeasible that brute force could be used to compromise a private key. To be able to spend their bitcoins, the owner must know the corresponding private key and digitally sign the transaction. The network verifies the signature using the public key.:ch. 5