Take the money on your bank account: What is it more than entries in a database that can only be changed under specific conditions? You can even take physical coins and notes: What are they else than limited entries in a public physical database that can only be changed if you match the condition than you physically own the coins and notes? Money is all about a verified entry in some kind of database of accounts, balances, and transactions.
Two members of the Silk Road Task Force—a multi-agency federal task force that carried out the U.S. investigation of Silk Road—seized bitcoins for their own use in the course of the investigation. DEA agent Carl Mark Force IV, who attempted to extort Silk Road founder Ross Ulbricht ("Dread Pirate Roberts"), pleaded guilty to money laundering, obstruction of justice, and extortion under color of official right, and was sentenced to 6.5 years in federal prison. U.S. Secret Service agent Shaun Bridges pleaded guilty to crimes relating to his diversion of $800,000 worth of bitcoins to his personal account during the investigation, and also separately pleaded guilty to money laundering in connection with another cryptocurrency theft; he was sentenced to nearly eight years in federal prison.
比特币与莱特币都采用了区块链技术，且都有51%攻击的问题。它们采用区块链技术，所有历史记录按照时间先后顺序，打包成一个个单独的区块，再把这些单独的区块链接在一起形成一个总账本  。这些区块内除了包含交易记录外，还包含新发行的莱特币和交易的手续费，这两笔钱支付给挖矿的矿工作为酬劳。无论谁挖到该区块，那么该区块内含有的新发行的莱特币和交易的手续费这两笔钱都归挖到者，以鼓励矿工积极参与结算。区块链技术容易产生51%攻击的问题：无论任何组织甚至个人，只要掌控某一种基于区块链原理的虚拟货币的全部运算能力的51%，这个人或组织就能够任意操纵该虚拟货币的所有交易。如果区块链只认运算能力最大者，谁的运算能力最大，谁就能抢到下一个区块，如果某个个人或组织掌控了全部运算能力的51%，那就意味着没人比他运算能力更强，故而他就可以随意操纵。所以，对于基于区块链原理的虚拟货币，参与挖矿的越多就越健壮，运算能力越分散就越健壮；挖坑者越少越脆弱，运算能力越集中就越脆弱，矿池越集中也就越脆弱  。
Cryptocurrencies are systems that allow for the secure payments of online transactions that are denominated in terms of a virtual "token," representing ledger entries internal to the system itself. "Crypto" refers to the fact that various encryption algorithms and cryptographic techniques, such as elliptical curve encryption, public-private key pairs, and hashing functions, are employed.
“If the trend continues, the average person will not be able to afford to purchase one whole bitcoin in 2 years. As global economies inflate and markets exhibit signs of recession, the world will turn to Bitcoin as a hedge against fiat turmoil and an escape against capital controls. Bitcoin is the way out, and cryptocurrency as a whole is never going away, it’s going to grow in use and acceptance as it matures.”
“Brave’s goal to reconnect users with creators and advertisers in order to fix the broken online ad system is now complete with the new Brave wallet, and we’re thrilled to have partnered with Uphold for this crucial development,” said Brendan Eich, CEO and co-founder of Brave. “The Brave browser offers unmatched speed, privacy, and most importantly an integrated wallet that rewards users and supports content creators, removing intermediaries that thrive on surveillance and fraud.”
Darknet markets present challenges in regard to legality. Bitcoins and other forms of cryptocurrency used in dark markets are not clearly or legally classified in almost all parts of the world. In the U.S., bitcoins are labelled as "virtual assets". This type of ambiguous classification puts pressure on law enforcement agencies around the world to adapt to the shifting drug trade of dark markets.
The validity of each cryptocurrency's coins is provided by a blockchain. A blockchain is a continuously growing list of records, called blocks, which are linked and secured using cryptography. Each block typically contains a hash pointer as a link to a previous block, a timestamp and transaction data. By design, blockchains are inherently resistant to modification of the data. It is "an open, distributed ledger that can record transactions between two parties efficiently and in a verifiable and permanent way". For use as a distributed ledger, a blockchain is typically managed by a peer-to-peer network collectively adhering to a protocol for validating new blocks. Once recorded, the data in any given block cannot be altered retroactively without the alteration of all subsequent blocks, which requires collusion of the network majority.
A lot of concerns have been raised regarding cryptocurrencies’ decentralized nature and their ability to be used almost completely anonymously. The authorities all over the world are worried about the cryptocurrencies’ appeal to the traders of illegal goods and services. Moreover, they are worried about their use in money laundering and tax evasion schemes.
In January 2015, the company received a US$75 million investment, led by Draper Fisher Jurvetson, the New York Stock Exchange, USAA, and several banks. Later in January, the company launched a U.S.-based bitcoin exchange for professional traders called Coinbase Exchange. Coinbase began to offer services in Canada in 2015, but in July 2016, Coinbase announced it would halt services in August after the closure of their Canadian online payments service provider Vogogo.
Many people believe that cryptocurrencies are the hottest investment opportunity currently available. Indeed, there are many stories of people becoming millionaires through their Bitcoin investments. Bitcoin is the most recognizable digital currency to date, and just last year one BTC was valued at $800. In November 2017, the price of one Bitcoin exceeded $7,000.
On 21 November 2017, the Tether cryptocurrency announced they were hacked, losing $31 million in USDT from their primary wallet. The company has 'tagged' the stolen currency, hoping to 'lock' them in the hacker's wallet (making them unspendable). Tether indicates that it is building a new core for its primary wallet in response to the attack in order to prevent the stolen coins from being used.