An online bitcoin wallet is a wallet hosted in the cloud. You access the wallet through a website, from any computer, where you can deposit and withdraw funds from your bitcoin wallet. The advantage is that you do not need to install any software on your computer or download the entire blockchain, which is currently more than 30 gigabyte. You can also access your wallet from any computer in the world. The disadvantage is that you are dependent on a third party service to store your bitcoins, which can be unstable, offline or even shut down.

Heath/Medical Records: Blockchain has the potential to standardize secure electronic medical record sharing across providers in a less burdensome way than previous approaches.5 It offers the ability to create a decentralized record management system that reduces the need for another organization between the patient and the records to manage access. Blockchain-enabled healthcare applications offer potential benefits such as instantly verifying the authenticity of prescriptions or automatically identifying potential adverse drug interactions.


Imagine this for a second, a hacker attacks block 3 and tries to change the data. Because of the properties of hash functions, a slight change in data will change the hash drastically. This means that any slight changes made in block 3, will change the hash which is stored in block 2, now that in turn will change the data and the hash of block 2 which will result in changes in block 1 and so on and so forth. This will completely change the chain, which is impossible. This is exactly how blockchains attain immutability.
By mining, you can earn cryptocurrency without having to put down money for it. That said, you certainly don't have to be a miner to own crypto.  You can also buy crypto using fiat currency (USD, EUR, JPY, etc); you can trade it on an exchange like Bitstamp using other crypto (example: Using Ethereum or NEO to buy Bitcoin); you even can earn it by playing video games or by publishing blogposts on platforms that pay its users in crypto. An example of the latter is Steemit, which is kind of like Medium except that users can reward bloggers by paying them in a proprietary cryptocurrency called Steem.  Steem can then be traded elsewhere for Bitcoin. 

A blockchain is a record-keeping system where multiple sources validate an entry before it gets added to the chain of data. Once data has been added, it cannot be changed and the record is distributed to multiple places within the network. Adding a new record (known as a block) to the blockchain sequence requires verification by multiple members connected to the blockchain network. These blocks of data are all linked to one another forming the chain. All transactions are public to those in the blockchain, but all individual identities are hidden.
The city of Zug in Switzerland uses a decentralized application (DAPP) for the verification of its citizens’ electronic identities. Another producer of DAPPs, for identity verification is Oraclize in Estonia. It markets a DAPP to solve the KYC (Know Your Customer) problem. This is of major importance in identity verification. The organization Thomson Reuters is creating another DAPP for identity verification using Ethereum.

In a traditional environment, trusted third parties act as intermediaries for financial transactions. If you have ever sent money overseas, it will pass through an intermediary (usually a bank). It will usually not be instantaneous (taking up to 3 days) and the intermediary will take a commission for doing this either in the form of exchange rate conversion or other charges.
User fear of 51% attacks can actually limit monopolies from forming on the blockchain. In “Digital Gold: Bitcoin and the Inside Story of the Misfits and Millionaires Trying to Reinvent Money,” New York Times journalist Nathaniel Popper writes of how a group of users, called “Bitfury,” pooled thousands of high-powered computers together to gain a competitive edge on the blockchain. Their goal was to mine as many blocks as possible and earn bitcoin, which at the time were valued at approximately $700 each.
The average price of a bitcoin can increase and decrease unpredictably. For example, in one week in November, 2015 Bitcoin went from $318 on a Monday to $492 on a Wednesday, falling back under $400 by Thursday.[14] Do not put too much money into bitcoin, as it's seen as a high-risk asset. Only buy enough bitcoins to make convenient online purchases.[15]

Here’s the ELI5 (“Explain it Like I’m 5”) version. You can think of a public key as a school locker and the private key as the locker combination. Teachers, students, and even your crush can insert letters and notes through the opening in your locker. However, the only person that can retrieve the contents of the mailbox is the one that has the unique key. It should be noted, however, that while school locker combinations are kept in the principal’s office, there is no central database that keeps track of a blockchain network’s private keys. If a user misplaces their private key, they will lose access to their Bitcoin wallet, as was the case with this man who made national headlines in December of 2017.
Blockchain is the underlying technology for digital currency like Bitcoin, Litecoin, and Ethereum and other digital properties. The technology records every transaction of a digital currency or property in a database or digital ledger. It also copies and distributes the database to a network of computers to validate each transaction. This decentralizes, secures, and publicizes each digital currency’s or property’s database of transactions.
With many practical applications for the technology already being implemented and explored, blockchain is finally making a name for itself at age twenty-seven, in no small part because of bitcoin and cryptocurrency. As a buzzword on the tongue of every investor in the nation, blockchain stands to make business and government operations more accurate, efficient, and secure.

A prospective miner needs a bitcoin wallet—an encrypted online bank account—to hold what is earned. The problem is, as in most bitcoin scenarios, wallets are unregulated and prone to attacks. Late last year, hackers staged a bitcoin heist in which they stole some $1.2 million worth of the currency from the site Inputs.io. When bitcoins are lost or stolen they are completely gone, just like cash. With no central bank backing your bitcoins, there is no possible way to recoup your loses.
Nakamoto is believed to have created the first blockchain database and has been the first to solve the double spending problem other digital currency failed to. While Bitcoin’s creator is shrouded in mystery, his Wizard of Oz status hasn’t stopped the digital currency from becoming increasingly popular with individuals, businesses, and even governments.
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Nigel Dodd argues in The Social Life of Bitcoin that the essence of the bitcoin ideology is to remove money from social, as well as governmental, control.[125] Dodd quotes a YouTube video, with Roger Ver, Jeff Berwick, Charlie Shrem, Andreas Antonopoulos, Gavin Wood, Trace Meyer and other proponents of bitcoin reading The Declaration of Bitcoin's Independence. The declaration includes a message of crypto-anarchism with the words: "Bitcoin is inherently anti-establishment, anti-system, and anti-state. Bitcoin undermines governments and disrupts institutions because bitcoin is fundamentally humanitarian."[125][124]
A blockchain carries no transaction cost. (An infrastructure cost yes, but no transaction cost.) The blockchain is a simple yet ingenious way of passing information from A to B in a fully automated and safe manner. One party to a transaction initiates the process by creating a block. This block is verified by thousands, perhaps millions of computers distributed around the net. The verified block is added to a chain, which is stored across the net, creating not just a unique record, but a unique record with a unique history. Falsifying a single record would mean falsifying the entire chain in millions of instances. That is virtually impossible. Bitcoin uses this model for monetary transactions, but it can be deployed in many others ways.
Imagine the number of legal documents that should be used that way. Instead of passing them to each other, losing track of versions, and not being in sync with the other version, why can’t *all* business documents become shared instead of transferred back and forth? So many types of legal contracts would be ideal for that kind of workflow. You don’t need a blockchain to share documents, but the shared documents analogy is a powerful one.” – William Mougayar, Venture advisor, 4x entrepreneur, marketer, strategist and blockchain specialist
Typically, consumers pay a bank to verify a transaction, a notary to sign a document, or a minister to perform a marriage. Blockchain eliminates the need for third-party verification and, with it, their associated costs. Business owners incur a small fee whenever they accept payments using credit cards, for example, because banks have to process those transactions. Bitcoin, on the other hand, does not have a central authority and has virtually no transaction fees.

The bitcoin blockchain is a public ledger that records bitcoin transactions.[67] It is implemented as a chain of blocks, each block containing a hash of the previous block up to the genesis block[a] of the chain. A network of communicating nodes running bitcoin software maintains the blockchain.[31]:215–219 Transactions of the form payer X sends Y bitcoins to payee Z are broadcast to this network using readily available software applications.
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