Обозначение Bitcoin

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Prices and value history
Among the factors which may have contributed to this rise were the European sovereign-debt crisis – particularly the 2012–2013 Cypriot financial crisis – statements by FinCEN improving the currency's legal standing, and rising media and Internet interest.

Until 2013, almost all market with bitcoins were in United States dollars (US$).

As the market valuation of the total stock of bitcoins approached US$1 billion, some commentators called bitcoin prices a bubble. In early April 2013, the price per bitcoin dropped from $266 to around $50 and then rose to around $100. Over two weeks starting late June 2013 the price dropped steadily to $70. The price began to recover, peaking once again on 1 October at $140. On 2 October, The Silk Road was seized by the FBI. This seizure caused a flash crash to $110. The price quickly rebounded, returning to $200 several weeks later. The latest run went from $200 on 3 November to $900 on 18 November. Bitcoin passed US$1,000 on 28 November 2013 at Mt. Gox.
Forks
See also: Bitcoin scalability problem and List of bitcoin forks
A fork referring to a blockchain is defined variously as a blockchain split into two paths forward, or as a change of protocol rules. Accidental forks on the bitcoin network regularly occur as part of the mining process. They happen when two miners find a block at a similar point in time. As a result, the network briefly forks. This fork is subsequently resolved by the software which automatically chooses the longest chain, thereby orphaning the extra blocks added to the shorter chain (that were dropped by the longer chain).

March 2013
On 12 March 2013, a bitcoin miner running version 0.8.0 of the bitcoin software created a large block that was considered invalid in version 0.7 (due to an undiscovered inconsistency between the two versions). This created a split or "fork" in the blockchain since computers with the recent version of the software accepted the invalid block and continued to build on the diverging chain, whereas older versions of the software rejected it and continued extending the blockchain without the offending block. This split resulted in two separate transaction logs being formed without clear consensus, which allowed for the same funds to be spent differently on each chain. In response, the Mt. Gox exchange temporarily halted bitcoin deposits. The exchange rate fell 23% to $37 on the Mt. Gox exchange but rose most of the way back to its prior level of $48.

Miners resolved the split by downgrading to version 0.7, putting them back on track with the canonical blockchain. User funds largely remained unaffected and were available when network consensus was restored. The network reached consensus and continued to operate as normal a few hours after the split.

August 2017
Two significant forks took place in August. One, Bitcoin Cash, is a hard fork off the main chain in opposition to the other, which is a soft fork to implement Segregated Witness.

Regulatory issues
On 18 March 2013, the Financial Crimes Enforcement Network (or FinCEN), a bureau of the United States Department of the Treasury, issued a report regarding centralized and decentralized "virtual currencies" and their legal status within "money services business" (MSB) and Bank Secrecy Act regulations. It classified digital currencies and other digital payment systems such as bitcoin as "virtual currencies" because they are not legal tender under any sovereign jurisdiction. FinCEN cleared American users of bitcoin of legal obligations by saying, "A user of virtual currency is not an MSB under FinCEN's regulations and therefore is not subject to MSB registration, reporting, and recordkeeping regulations." However, it held that American entities who generate "virtual currency" such as bitcoins are money transmitters or MSBs if they sell their generated currency for national currency: "...a person that creates units of convertible virtual currency and sells those units to another person for real currency or its equivalent is engaged in transmission to another location and is a money transmitter." This specifically extends to "miners" of the bitcoin currency who may have to register as MSBs and abide by the legal requirements of being a money transmitter if they sell their generated bitcoins for national currency and are within the United States. Since FinCEN issued this guidance, dozens of virtual currency exchangers and administrators have registered with FinCEN, and FinCEN is receiving an increasing number of suspicious activity reports (SARs) from these entities.

Additionally, FinCEN claimed regulation over American entities that manage bitcoins in a payment processor setting or as an exchanger: "In addition, a person is an exchanger and a money transmitter if the person accepts such de-centralized convertible virtual currency from one person and transmits it to another person as part of the acceptance and transfer of currency, funds, or other value that substitutes for currency."

In summary, FinCEN's decision would require bitcoin exchanges where bitcoins are traded for traditional currencies to disclose large transactions and suspicious activity, comply with money laundering regulations, and collect information about their customers as traditional financial institutions are required to do.

Jennifer Shasky Calvery, the director of FinCEN said, "Virtual currencies are subject to the same rules as other currencies. ... Basic money-services business rules apply here."

In its October 2012 study, Virtual currency schemes, the European Central Bank concluded that the growth of virtual currencies will continue, and, given the currencies' inherent price instability, lack of close regulation, and risk of illegal uses by anonymous users, the Bank warned that periodic examination of developments would be necessary to reassess risks.

In 2013, the U.S. Treasury extended its anti-money laundering regulations to processors of bitcoin transactions.

In June 2013, Bitcoin Foundation board member Jon Matonis wrote in Forbes that he received a warning letter from the California Department of Financial Institutions accusing the foundation of unlicensed money transmission. Matonis denied that the foundation is engaged in money transmission and said he viewed the case as "an opportunity to educate state regulators."

In late July 2013, the industry group Committee for the Establishment of the Digital Asset Transfer Authority began to form to set best practices and standards, to work with regulators and policymakers to adapt existing currency requirements to digital currency technology and business models and develop risk management standards.

In 2014, the U.S. Securities and Exchange Commission filed an administrative action against Erik T. Voorhees, for violating Securities Act Section 5 for publicly offering unregistered interests in two bitcoin websites in exchange for bitcoins.

By December 2017, bitcoin futures contracts began to be offered, and the US Chicago Board Options Exchange (CBOE) was formally settling the futures daily. By 2019, multiple trading companies were offering services around bitcoin futures.

Bitcoin faucets
A bitcoin faucet is a reward system, in the form of a website or software app, that dispenses rewards in the form of a satoshi, which is worth a hundredth of a millionth BTC, for visitors to claim in exchange for completing a captcha or task as described by the website. There are also faucets that dispense alternative cryptocurrencies. The first bitcoin faucet was called "The Bitcoin Faucet" and was developed by Gavin Andresen in 2010. It originally gave out five bitcoins per person.

The rewards are dispensed at various predetermined intervals of time as rewards for completing simple tasks such as captcha completion and as prizes from simple games. Faucets usually give fractions of a bitcoin, but the amount will typically fluctuate according to the value of bitcoin. Some faucets also have random larger rewards. To reduce mining fees, faucets normally save up these small individual payments in their own ledgers, which then add up to make a larger payment that is sent to a user's bitcoin address.

Because bitcoin transactions are irreversible and there are many faucets, they have become targets for hackers interested in stealing bitcoins. Advertisements are the main income source of bitcoin faucets. Faucets try to get traffic from users by offering free bitcoin as an incentive. Some ad networks also pay directly in bitcoin. This means that faucets often have a low profit margin. Some faucets also make money by mining altcoin in the background, using the user's CPU.

Theft and exchange shutdowns
Bitcoins can be stored in a bitcoin cryptocurrency wallet. Theft of bitcoin has been documented on numerous occasions. At other times, bitcoin exchanges have shut down, taking their clients' bitcoins with them. A Wired study published April 2013 showed that 45 percent of bitcoin exchanges end up closing.

On 19 June 2011, a security breach of the Mt. Gox bitcoin exchange caused the nominal price of a bitcoin to fraudulently drop to one cent on the Mt. Gox exchange, after a hacker used credentials from a Mt. Gox auditor's compromised computer illegally to transfer a large number of bitcoins to himself. They used the exchange's software to sell them all nominally, creating a massive "ask" order at any price. Within minutes, the price reverted to its correct user-traded value. Accounts with the equivalent of more than US$8,750,000 were affected.

In July 2011, the operator of Bitomat, the third-largest bitcoin exchange, announced that he had lost access to his wallet.dat file with about 17,000 bitcoins (roughly equivalent to US$220,000 at that time). He announced that he would sell the service for the missing amount, aiming to use funds from the sale to refund his customers.

In August 2011, MyBitcoin, a now defunct bitcoin transaction processor, declared that it was hacked, which caused it to be shut down, paying 49% on customer deposits, leaving more than 78,000 bitcoins (equivalent to roughly US$800,000 at that time) unaccounted for.

In early August 2012, a lawsuit was filed in San Francisco court against Bitcoinica – a bitcoin trading venue – claiming about US$460,000 from the company. Bitcoinica was hacked twice in 2012, which led to allegations that the venue neglected the safety of customers' money and cheated them out of withdrawal requests.

In late August 2012, an operation titled Bitcoin Savings and Trust was shut down by the owner, leaving around US$5.6 million in bitcoin-based debts; this led to allegations that the operation was a Ponzi scheme. In September 2012, the U.S. Securities and Exchange Commission had reportedly started an investigation on the case.

In September 2012, Bitfloor, a bitcoin exchange, also reported being hacked, with 24,000 bitcoins (worth about US$250,000) stolen. As a result, Bitfloor suspended operations. The same month, Bitfloor resumed operations; its founder said that he reported the theft to FBI, and that he plans to repay the victims, though the time frame for repayment is unclear.

On 3 April 2013, Instawallet, a web-based wallet provider, was hacked, resulting in the theft of over 35,000 bitcoins which were valued at US$129.90 per bitcoin at the time, or nearly $4.6 million in total. As a result, Instawallet suspended operations.

On 11 August 2013, the Bitcoin Foundation announced that a bug in a pseudorandom number generator within the Android operating system had been exploited to steal from wallets generated by Android apps; fixes were provided 13 August 2013.

In October 2013, Inputs.io, an Australian-based bitcoin wallet provider was hacked with a loss of 4100 bitcoins, worth over A$1 million at time of theft. The service was run by the operator TradeFortress. Coinchat, the associated bitcoin chat room, was taken over by a new admin.

On 26 October 2013, a Hong Kong–based bitcoin trading platform owned by Global Bond Limited (GBL) vanished with 30 million yuan (US$5 million) from 500 investors.

Mt. Gox, the Japan-based exchange that in 2013 handled 70% of all worldwide bitcoin traffic, declared bankruptcy in February 2014, with bitcoins worth about $390 million missing, for unclear reasons. The CEO was eventually arrested and charged with embezzlement.

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.

Chinese cryptocurrency exchange Bter lost $2.1 million in BTC in February 2015.

The Slovenian exchange Bitstamp lost bitcoin worth $5.1 million to a hack in January 2015.

The US-based exchange Cryptsy declared bankruptcy in January 2016, ostensibly because of a 2014 hacking incident; the court-appointed receiver later alleged that Cryptsy's CEO had stolen $3.3 million.

In August 2016, hackers stole some $72 million in customer bitcoin from the Hong Kong–based exchange Bitfinex.

In December 2017, hackers stole 4,700 bitcoins from NiceHash a platform that allowed users to sell hashing power. The value of the stolen bitcoins totaled about $80M.

On 19 December 2017, Yapian, a company that owns the Youbit cryptocurrency exchange in South Korea, filed for bankruptcy following a hack, the second in eight months.

Taxation and regulation
See also: Legality of bitcoin by country or territory
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."

In August 2013, the German Finance Ministry characterized bitcoin as a unit of account, usable in multilateral clearing circles and subject to capital gains tax if held less than one year.

On 5 December 2013, the People's Bank of China announced in a press release regarding bitcoin regulation that whilst individuals in China are permitted to freely trade and exchange bitcoins as a commodity, it is prohibited for Chinese financial banks to operate using bitcoins or for bitcoins to be used as legal tender currency, and that entities dealing with bitcoins must track and report suspicious activity to prevent money laundering. The value of bitcoin dropped on various exchanges between 11 and 20 percent following the regulation announcement, before rebounding upward again.

Arbitrary blockchain content
Bitcoin's blockchain can be loaded with arbitrary data. In 2018 researchers from RWTH Aachen University and Goethe University identified 1,600 files added to the blockchain, 59 of which included links to unlawful images of child exploitation, politically sensitive content, or privacy violations. "Our analysis shows that certain content, e.g. illegal pornography, can render the mere possession of a blockchain illegal."

Interpol also sent out an alert in 2015 saying that "the design of the blockchain means there is the possibility of malware being injected and permanently hosted with no methods currently available to wipe this data".