History of bitcoin

Prior to the release of bitcoin, there were a number of digital cash technologies, starting with the issuer-based ecash protocols of David Chaum and Stefan Brands. The idea that solutions to computational puzzles could have some value was first proposed by cryptographers Cynthia Dwork and Moni Naor in 1992. 31 October 1996 NSA paper 12 years prior to creating Bitcoin the NSA published the white paper "How To Make A Mint: The Cryptography of Anonymous Electronic Cash" Adam Back The idea was independently rediscovered by Adam Back who developed hashcash, a proof-of-work scheme for spam control in 1997. The first proposals for distributed digital scarcity-based cryptocurrencies were Wei Dai's b-money and Nick Szabo's bit gold. Hal Finney developed reusable proof of work (RPOW) using hashcash as proof of work algorithm. In the bit gold proposal which proposed a collectible market-based mechanism for inflation control, Nick Szabo also investigated some additional aspects including a Byzantine fault-tolerant agreement protocol based on quorum addresses to store and transfer the chained proof-of-work solutions, which was vulnerable to Sybil attacks, though. ==Creation==

On 18 August 2008, the domain name bitcoin.org was registered. Later that year, on 31 October, a link to a paper authored by Satoshi Nakamoto titled Bitcoin: A Peer-to-Peer Electronic Cash System was posted to a cryptography mailing list. This paper detailed methods of using a peer-to-peer network to generate what was described as "a system for electronic transactions without relying on trust". On 3 January 2009, the bitcoin network came into existence with Satoshi Nakamoto mining the genesis block of bitcoin (block number 0), which had a reward of 50 bitcoins. Embedded in the genesis block was the text: The Times 03/Jan/2009 Chancellor on brink of second bailout for banks The text refers to a headline in The Times published on 3 January 2009. This note has been interpreted as both a timestamp of the genesis date and a derisive comment on the instability caused by fractional-reserve banking. The first open source bitcoin client was released on 9 January 2009, hosted at SourceForge. One of the first supporters, adopters, contributors to bitcoin and receiver of the first bitcoin transaction was programmer Hal Finney. Finney downloaded the bitcoin software the day it was released, and received 10 bitcoins from Nakamoto in the world's first bitcoin transaction on 12 January 2009 (block 170). Other early supporters were Wei Dai, creator of bitcoin predecessor b-money, and Nick Szabo, creator of bitcoin predecessor bit gold. Blockchain analyst Sergio Demian Lerner estimated in 2013 that Satoshi Nakamoto mined approximately 1 million bitcoins during the network's first year, based on a distinct pattern in early blocks dubbed the "Patoshi pattern". Other analyses, including a 2018 estimate by BitMEX Research, place the figure lower at around 600,000–700,000 bitcoins. Before disappearing from any involvement in bitcoin, Nakamoto in a sense handed over the reins to developer Gavin Andresen, who then became the bitcoin lead developer at the Bitcoin Foundation, the 'anarchic' bitcoin community's closest thing to an official public face. Satoshi Nakamoto "Satoshi Nakamoto" is presumed to be a pseudonym for the person or people who designed the original bitcoin protocol in 2007 then released the whitepaper in 2008 and finally launched the network in 2009. Nakamoto was responsible for creating the majority of the official bitcoin software and was active in making modifications and posting technical information on the bitcoin forum. There has been much speculation as to the identity of Satoshi Nakamoto and their real identity remains a matter of dispute. ==Growth==

2010 franchise on Atlantic Blvd in Jacksonville, Florida, where two pizzas were made and delivered from for the first notable retail bitcoin transaction. The first notable retail transaction involving physical goods took place on 22 May 2010. Laszlo Hanyecz, a programmer in Jacksonville, Florida, posted on the Bitcointalk forum offering 10,000 of his mined bitcoins in exchange for two pizzas. A 19-year-old in California named Jeremy Sturdivant accepted the offer and ordered two Papa John's pizzas for delivery to Hanyecz's home, receiving the 10,000 BTC in exchange. At the time, the bitcoins were worth around $41. The date is commemorated annually as "Bitcoin Pizza Day". On 6 August 2010, a major vulnerability in the bitcoin protocol was spotted. While the protocol did verify that a transaction's outputs never exceeded its inputs, a transaction whose outputs summed to more than 2^{64} would overflow, permitting the transaction author to create arbitrary amounts of bitcoin. Since the blockchain was forked below the problematic transaction, the transaction no longer appears in the blockchain used by the current Bitcoin network. 2011 Based on bitcoin's open-source code, other cryptocurrencies started to emerge. The Electronic Frontier Foundation, a non-profit group, started accepting bitcoins in January 2011, then stopped accepting them in June 2011, citing concerns about a lack of legal precedent about new currency systems. The EFF's decision was reversed on 17 May 2013 when they resumed accepting bitcoin. In May 2011, bitcoin payment processor, BitPay was founded to provide mobile checkout services to companies wanting to accept bitcoins as a form of payment. In June 2011, WikiLeaks In September 2012, the Bitcoin Foundation was launched to "accelerate the global growth of bitcoin through standardization, protection, and promotion of the open source protocol". The founders were Gavin Andresen, Jon Matonis, Mark Karpelès, Charlie Shrem, and Peter Vessenes. In October 2012, BitPay reported having over 1,000 merchants accepting bitcoin under its payment processing service. In November 2012, WordPress started accepting bitcoins. 2013 In February 2013, the exchange Coinbase reported selling US$1 million worth of bitcoins in a single month at over $22 per bitcoin. The Internet Archive announced that it was ready to accept donations as bitcoins and that it intends to give employees the option to receive portions of their salaries in bitcoin currency. In Charles Stross's 2013 science fiction novel ''Neptune's Brood, the universal interstellar payment system is known as "bitcoin" and operates using cryptography. Stross later blogged that the reference was intentional, saying "I wrote Neptune's Brood'' in 2011. Bitcoin was obscure back then, and I figured had just enough name recognition to be a useful term for an interstellar currency: it'd clue people in that it was a networked digital currency." In March, the bitcoin transaction log, called the blockchain, temporarily split into two independent chains with differing rules on how transactions were accepted. For six hours two bitcoin networks operated at the same time, each with its own version of the transaction history. The core developers called for a temporary halt to transactions, sparking a sharp sell-off. The Mt. Gox exchange briefly halted bitcoin deposits and the exchange rate briefly dipped by 23% to $37 as the event occurred In the US, the Financial Crimes Enforcement Network (FinCEN) established regulatory guidelines for "decentralized virtual currencies" such as bitcoin, classifying American bitcoin miners who sell their generated bitcoins as Money Service Businesses (or MSBs), that may be subject to registration and other legal obligations. In April, payment processors BitInstant and Mt. Gox experienced processing delays due to insufficient capacity resulting in the bitcoin exchange rate dropping from $266 to $76 before returning to $160 within six hours. Bitcoin gained greater recognition when services such as OkCupid and Foodler began accepting it for payment. In April 2013, Eric Posner, a law professor at the University of Chicago, stated that "a real Ponzi scheme takes fraud; bitcoin, by contrast, seems more like a collective delusion." On 15 May 2013, the US authorities seized accounts associated with Mt. Gox after discovering that it had not registered as a money transmitter with FinCEN in the US. On 17 May 2013, it was reported that BitInstant processed approximately 30 percent of the money going into and out of bitcoin, and in April alone facilitated 30,000 transactions, On 23 June 2013, it was reported that the US Drug Enforcement Administration listed 11.02 bitcoins as a seized asset in a United States Department of Justice seizure notice pursuant to 21 U.S.C. § 881. This was the first time a government agency was reported to have seized bitcoin. 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. On 6 August 2013, Federal Judge Amos Mazzant of the Eastern District of Texas of the Fifth Circuit ruled that bitcoins are "a currency or a form of money" (specifically securities as defined by Federal Securities Laws), and as such were subject to the court's jurisdiction, and Germany's Finance Ministry subsumed bitcoins under the term "unit of account" a financial instrument though not as e-money or a functional currency, a classification nonetheless having legal and tax implications. In September 2013, Chinese Govt. banned financial institution from trading in Bitcoin fearing a risk of money laundering. In October 2013, the FBI seized roughly 26,000 BTC from website Silk Road during the arrest of alleged owner Ross William Ulbricht. Two companies, Robocoin and Bitcoiniacs launched the world's first bitcoin ATM on 29 October 2013 in Vancouver, BC, Canada, allowing clients to sell or purchase bitcoin currency at a downtown coffee shop. Chinese internet giant Baidu had allowed clients of website security services to pay with bitcoins. In November 2013, the University of Nicosia announced that it would be accepting bitcoin as payment for tuition fees. During November 2013, the China-based bitcoin exchange BTC China overtook the Japan-based Mt. Gox and the Europe-based Bitstamp to become the largest bitcoin trading exchange by trade volume. In December 2013, Overstock.com announced plans to accept bitcoin in the second half of 2014. On 5 December 2013, the People's Bank of China prohibited Chinese financial institutions from using bitcoins. After the announcement, the value of bitcoins dropped, and Baidu no longer accepted bitcoins for certain services. Buying real-world goods with any virtual currency had been illegal in China since at least 2009. On 4 December 2013, Alan Greenspan referred to it as a "bubble". 2014 In January 2014, Zynga announced it was testing bitcoin for purchasing in-game assets in seven of its games. That same month, The D Las Vegas Casino Hotel and Golden Gate Hotel & Casino properties in downtown Las Vegas announced they would also begin accepting bitcoin, according to an article by USA Today. The article also stated the currency would be accepted in five locations, including the front desk and certain restaurants. The network rate exceeded 10 petahash/sec. TigerDirect and Overstock.com started accepting bitcoin. The same month, an operator of a U.S. bitcoin exchange, Robert Faiella better known as Charlie Shrem, was arrested for money laundering. In early February 2014, one of the largest bitcoin exchanges, Mt. Gox, suspended withdrawals citing technical issues. By the end of the month, Mt. Gox had filed for bankruptcy protection in Japan amid reports that 744,000 bitcoins had been stolen. Months before the filing, the popularity of Mt. Gox had waned as users experienced difficulties withdrawing funds. In June 2014, the network exceeded 100 petahash/sec. On 18 June 2014, it was announced that bitcoin payment service provider BitPay would become the new sponsor of St. Petersburg Bowl under a two-year deal, renamed the Bitcoin St. Petersburg Bowl. Bitcoin was to be accepted for ticket and concession sales at the game as part of the sponsorship, and the sponsorship itself was also paid for using bitcoin. In July 2014, Newegg and Dell started accepting bitcoin. In September 2014, TeraExchange, LLC, received approval from the U.S. Commodity Futures Trading Commission "CFTC" to begin listing an over-the-counter swap product based on the price of a bitcoin. The CFTC swap product approval marks the first time a U.S. regulatory agency approved a bitcoin financial product. In December 2014, Microsoft began to accept bitcoin to buy Xbox games and Windows software. In 2014, several light-hearted songs celebrating bitcoin such as the "Ode to Satoshi" were released. A documentary film, The Rise and Rise of Bitcoin, was released in 2014, featuring interviews with bitcoin users such as a computer programmer and a drug dealer. On 13 March 2014, Warren Buffett called bitcoin a "mirage". 2015 In January 2015, Coinbase raised US$75 million as part of a Series C funding round, smashing the previous record for a bitcoin company. Less than one year after the collapse of Mt. Gox, United Kingdom-based exchange Bitstamp announced that their exchange would be taken offline while they investigate a hack which resulted in about 19,000 bitcoins (equivalent to roughly US$5 million at that time) being stolen from their hot wallet. The exchange remained offline for several days amid speculation that customers had lost their funds. Bitstamp resumed trading on 9 January after increasing security measures and assuring customers that their account balances would not be impacted. In February 2015, the number of merchants accepting bitcoin exceeded 100,000. In 2015, the MAK (Museum of Applied Arts, Vienna) became the first museum to acquire art using bitcoin, when it purchased the screensaver "Event listeners" of van den Dorpel. In September 2015, the establishment of the peer-reviewed academic journal Ledger () was announced. It covers studies of cryptocurrencies and related technologies, and is published by the University of Pittsburgh. In October 2015, a proposal was submitted to the Unicode Consortium to add a code point for the bitcoin symbol. 2016 In January 2016, the network rate exceeded 1 exahash/sec. In March 2016, the Cabinet of Japan recognized virtual currencies like bitcoin as having a function similar to real money. In July 2016, the CheckSequenceVerify soft fork activated. In August 2016, a major bitcoin exchange, Bitfinex, was hacked and nearly 120,000 BTC (around $60m) was stolen. 2017 In January 2017, NHK reported the number of online stores accepting bitcoin in Japan had increased 4.6 times over the past year. In April, Japan passes a law to accept bitcoin as a legal payment method. Russia announces that it will legalize the use of cryptocurrencies such as bitcoin. In June 2017, the bitcoin symbol was encoded in Unicode version 10.0 at position U+20BF (₿) in the Currency Symbols block. Up until July 2017, bitcoin users maintained a common set of rules for the cryptocurrency. On 1 August 2017 bitcoin split into two derivative digital currencies, the bitcoin (BTC) chain with 1 MB blocksize limit and the Bitcoin Cash (BCH) chain with 8 MB blocksize limit. The split has been called the Bitcoin Cash hard fork. On 6 December 2017 the software marketplace Steam announced that it would no longer accept bitcoin as payment for its products, citing slow transactions speeds, price volatility, and high fees for transactions. 2018 On 22 January 2018, South Korea brought in a regulation that requires all the bitcoin traders to reveal their identity, thus putting a ban on anonymous trading of bitcoins. On 24 January 2018, the online payment firm Stripe announced that it would phase out its support for bitcoin payments by late April 2018, citing declining demand, rising fees and longer transaction times as the reasons. On 25 January 2018, George Soros referred to bitcoin as a bubble. In May 2018, the United States Department of Justice investigated bitcoin traders for possible price manipulation, focusing on practices like spoofing and wash trades. The investigation, which involved key exchanges like Bitstamp, Coinbase, and Kraken, led to subpoenas from the Commodity Futures Trading Commission after these exchanges failed to comply with information requests. In October 2018, Nelson Saiers installed a 9-foot inflatable rat covered with bitcoin references and code in front of the Federal Reserve as a homage to Satoshi Nakamoto and protests in New York City. 2020 On 2 July 2020, the Swiss company 21Shares started to quote a set of bitcoin exchange-traded products (ETP) on the Xetra trading system of the Deutsche Boerse. On 1 September 2020, the Wiener Börse listed its first 21 titles denominated in cryptocurrencies like bitcoin, including the services of real-time quotation and securities settlement. On 3 September 2020, the Frankfurt Stock Exchange admitted in its Regulated Market the quotation of the first bitcoin exchange-traded note (ETN), centrally cleared via Eurex Clearing. In October 2020, PayPal announced that it would allow its users to buy and sell bitcoin on its platform, although not to deposit or withdraw bitcoins. 2021 On 19 January 2021, Elon Musk placed the handle #Bitcoin in his Twitter profile, tweeting "In retrospect, it was inevitable", which caused the price to briefly rise about $5,000 in an hour to $37,299. On 25 January 2021, Microstrategy announced that it continued to buy bitcoin and as of the same date it had holdings of ₿70,784 worth $2.38 billion. On 8 February 2021 Tesla's announcement of a bitcoin purchase of US$1.5 billion and the plan to start accepting bitcoin as payment for vehicles, pushed the bitcoin price to $44,141. On 18 February 2021, Elon Musk stated that "owning bitcoin was only a little better than holding conventional cash, but that the slight difference made it a better asset to hold". After 49 days of accepting the digital currency, Tesla reversed course on 12 May 2021, saying they would no longer take bitcoin due to concerns that "mining" the cryptocurrency was contributing to the consumption of fossil fuels and climate change. The decision resulted in the price of bitcoin dropping around 12% on 13 May. During a July bitcoin conference, Musk suggested Tesla could possibly help bitcoin miners switch to renewable energy in the future and also stated at the same conference that if bitcoin mining reaches, and trends above 50 percent renewable energy usage, that "Tesla would resume accepting bitcoin." The price for bitcoin rose after this announcement. From February 2021, the Swiss canton of Zug allows for tax payments in bitcoin and other cryptocurrencies. Bitcoin achieved price equivalence with one kilogram of gold. In May 2021, Tesla suspends Bitcoin payments due to environmental concerns, causing a significant market reaction. On 1 June 2021, El Salvador President Nayib Bukele announced his plans to adopt bitcoin as legal tender; this would render El Salvador the world's first country to do so. On June 7, 2021, United States Justice Department recovered $2.3 million worth of bitcoin paid by Colonial Pipeline to a criminal cyber group in cyber-security ransom. On 8 June 2021, at the initiative of the president, pro-government deputies in the Legislative Assembly of El Salvador voted legislation—Ley Bitcoin or the Bitcoin Law—to make Bitcoin legal tender in the country alongside the US Dollar. 2022 On April 22, 2022, its price fell back down below $40,000. It further dropped to as low as $26,970 in May after the collapse of Terra-Luna and its sister stablecoin, UST, in addition to a shedding of tech stocks. On 18 June, Bitcoin dropped below $18,000, to trade at levels beneath its 2017 highs. In May 2022, following a vote by Wikipedia editors the previous month, the Wikimedia Foundation announced it would stop accepting donations in bitcoin or other cryptocurrencies—eight years after it had first started taking contributions in bitcoin. 2023 In 2023, ordinals, non-fungible tokens (NFTs) on Bitcoin, went live. 2024 In 2024, bitcoin-holding ETF funds were approved. On March 13, 2024, Bitcoin price reached $73,664 USD. In April 2024, the fourth bitcoin halving occurred, meaning that the reward to miners for successfully completing a block dropped to 3.125 bitcoins from 6.25 bitcoins. ==Prices and value history==

). Among the factors which may have contributed to this rise were the European sovereign-debt crisisparticularly the 2012–2013 Cypriot financial crisisstatements 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==

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. == Taxation and regulation ==

2012 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 April 2012 the FBI acknowledged Bitcoin's potential for illicit use in an internal assessment. The report identified Bitcoin’s decentralized and pseudonymous design as a challenge for law enforcement, noting early signs of adoption by cybercriminals despite limited evidence of widespread misuse. Although it warned of high theft risks via malware and wallet exploitation, it concluded only with low confidence that, "based on current user and vendor acceptance, that malicious actors will exploit Bitcoin to launder money". The report highlighted third-party exchanges as regulatory choke points under U.S. law, marking one of the first federal acknowledgments of the systemic enforcement difficulties posed by cryptocurrencies. 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. 2013 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. 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." 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 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 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. The value of bitcoin dropped on various exchanges between 11 and 20 percent following the regulation announcement, before rebounding upward again. In 2013, the U.S. Treasury extended its anti-money laundering regulations to processors of bitcoin transactions. 2014 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. On 25 March 2014, the U.S. Internal Revenue Service issued Notice 2014-21, clarifying that for federal tax purposes, virtual currency is treated as property, not currency. 2016 In 2016, the European Parliament began discussions to bring virtual currency exchanges and custodian wallet providers under the scope of the Anti-Money Laundering Directive (AMLD). The proposal was published in July 2016, marking "a significant step in the EU's efforts to combat the laundering of money from criminal activities and to counter the financing of terrorist activities." 2017 By December 2017, bitcoin futures contracts began to be offered, and the US Chicago Board Options Exchange (CBOE) was formally settling the futures daily. 2019 By 2019, multiple trading companies were offering services around bitcoin futures. ==Bitcoin faucets==

A bitcoin faucet was a website or software app that dispensed rewards in the form of bitcoin for visitors to claim in exchange for completing a captcha or task as described by the website. There have also been faucets that dispense other cryptocurrencies. The first example was called "The Bitcoin Faucet" and was developed by Gavin Andresen in 2010. It originally gave out five bitcoins per person. The rewards were dispensed at regular time intervals as rewards for completing simple tasks such as captcha completion, or as prizes from simple games. The amount of bitcoin would typically fluctuate according to the cash value of bitcoin. Some faucets also had random larger rewards. To reduce mining fees, faucets saved up these small individual payments in their own ledgers, which would be dispersed as larger payment to a user's bitcoin address. Because bitcoin transactions are irreversible and there have been many faucets, they have been targets for hackers interested in acquiring bitcoins through theft or exploitation. Advertisements were the main income source of bitcoin faucets, with the potential reward in cryptocurrency intended to incentivize traffic. Some ad networks have also paid directly in bitcoin. Faucets typically have a low profit margin. Some faucets have also made money by mining cryptocurrencies 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. Accounts with the equivalent of more than US$8,750,000 were affected. 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 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 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. 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 $80 million at the time. 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. On 11 November 2022, FTX filed for bankruptcy with an estimated $8 billion missing in customer funds. ==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". ==References==