The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and the media.[226] In the United States, the FBI prepared an intelligence assessment,[227] the SEC issued a pointed warning about investment schemes using virtual currencies,[226] and the U.S. Senate held a hearing on virtual currencies in November 2013.[228] The U.S. government claimed that bitcoin was used to facilitate payments related to Russian interference in the 2016 United States elections.[229]
The use of bitcoin by criminals has attracted the attention of financial regulators, legislative bodies, law enforcement, and the media.[226] In the United States, the FBI prepared an intelligence assessment,[227] the SEC issued a pointed warning about investment schemes using virtual currencies,[226] and the U.S. Senate held a hearing on virtual currencies in November 2013.[228] The U.S. government claimed that bitcoin was used to facilitate payments related to Russian interference in the 2016 United States elections.[229]

Physical wallets store the credentials necessary to spend bitcoins offline and can be as simple as a paper printout of the private key:[7]:ch. 10 a paper wallet. A paper wallet is created with a keypair generated on a computer with no internet connection; the private key is written or printed onto the paper[h] and then erased from the computer. The paper wallet can then be stored in a safe physical location for later retrieval. Bitcoins stored using a paper wallet are said to be in cold storage.[104]:39 In a 2014 interview, QuadrigaCX founder Gerald Cotten explained that the company stored customer funds on paper wallets in safe deposit boxes: "So we just send money to them, we don’t need to go back to the bank every time we want to put money into it. We just send money from our Bitcoin app directly to those paper wallets, and keep it safe that way."[105]

While another less aggressive soft fork solution was put forth, the Ethereum community and its founders were placed in a perilous position. If they didn’t retrieve the stolen investor money, confidence in Ethereum could be lost. On the other hand, recovering investor money required actions that went against the core ideas of decentralization and set a dangerous precedent.
An initial coin offering (ICO) is a controversial means of raising funds for a new cryptocurrency venture. An ICO may be used by startups with the intention of avoiding regulation. However, securities regulators in many jurisdictions, including in the U.S., and Canada have indicated that if a coin or token is an "investment contract" (e.g., under the Howey test, i.e., an investment of money with a reasonable expectation of profit based significantly on the entrepreneurial or managerial efforts of others), it is a security and is subject to securities regulation. In an ICO campaign, a percentage of the cryptocurrency (usually in the form of "tokens") is sold to early backers of the project in exchange for legal tender or other cryptocurrencies, often bitcoin or ether.[47][48][49]
The term altcoin has various similar definitions. Stephanie Yang of The Wall Street Journal defined altcoins as "alternative digital currencies,"[20] while Paul Vigna, also of The Wall Street Journal, described altcoins as alternative versions of bitcoin.[21] Aaron Hankins of the MarketWatch refers to any cryptocurrencies other than bitcoin as altcoins.[22]
In 1998, Wei Dai published a description of "b-money", characterized as an anonymous, distributed electronic cash system.[12] Shortly thereafter, Nick Szabo described bit gold.[13] Like bitcoin and other cryptocurrencies that would follow it, bit gold (not to be confused with the later gold-based exchange, BitGold) was described as an electronic currency system which required users to complete a proof of work function with solutions being cryptographically put together and published. A currency system based on a reusable proof of work was later created by Hal Finney who followed the work of Dai and Szabo.[citation needed]
Ethereum-based customized software and networks, independent from the public Ethereum chain, are being tested by enterprise software companies.[47] Interested parties include Microsoft, IBM, JPMorgan Chase,[33][48] Deloitte,[49] R3,[50] Innovate UK (cross-border payments prototype).[51] Barclays, UBS and Credit Suisse are experimenting with Ethereum.
In cryptocurrency networks, mining is a validation of transactions. For this effort, successful miners obtain new cryptocurrency as a reward. The reward decreases transaction fees by creating a complementary incentive to contribute to the processing power of the network. The rate of generating hashes, which validate any transaction, has been increased by the use of specialized machines such as FPGAs and ASICs running complex hashing algorithms like SHA-256 and Scrypt.[30] This arms race for cheaper-yet-efficient machines has been on since the day the first cryptocurrency, bitcoin, was introduced in 2009.[30] With more people venturing into the world of virtual currency, generating hashes for this validation has become far more complex over the years, with miners having to invest large sums of money on employing multiple high performance ASICs. Thus the value of the currency obtained for finding a hash often does not justify the amount of money spent on setting up the machines, the cooling facilities to overcome the enormous amount of heat they produce, and the electricity required to run them.[30][31]
In 2014, researchers at the University of Kentucky found "robust evidence that computer programming enthusiasts and illegal activity drive interest in bitcoin, and find limited or no support for political and investment motives".[140] Australian researchers have estimated that 25% of all bitcoin users and 44% of all bitcoin transactions are associated with illegal activity as of April 2017. There were an estimated 24 million bitcoin users primarily using bitcoin for illegal activity. They held $8 billion worth of bitcoin, and made 36 million transactions valued at $72 billion.[233][234]
Bitcoin has been criticized for its use in illegal transactions, its high electricity consumption, price volatility, and thefts from exchanges. Some noted economists, including several Nobel laureates, have characterized it as a speculative bubble. Bitcoin has also been used as an investment, although several regulatory agencies have issued investor alerts about bitcoin.[19][20]
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