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.
Once the recording of a transaction is on the Blockchain and the Blockchain has been updated, then the alteration of the records of this transaction is impossible. This is due to that particular transaction record being linked to the record of every preceding one. Blockchain records are permanent, they are ordered chronologically, and they are available to all the other nodes. The diagram shows an extract from the Bitcoin Blockchain.

The technological complexity is explained nicely to a degree which is necessary for the user to understand roughly the whole block chain as a system. Explaining a car and its advantages for humans would start also by describing wheels, motor and steering by hand. A car user does not need to know the details of a motor , electricity etc. He looks at how to move, security, velocity etc.
An official investigation into bitcoin traders was reported in May 2018.[173] The U.S. Justice Department launched an investigation into possible price manipulation, including the techniques of spoofing and wash trades.[174][175][176] Traders in the U.S., the U.K, South Korea, and possibly other countries are being investigated.[173] Brett Redfearn, head of the U.S. Securities and Exchange Commission's Division of Trading and Markets, had identified several manipulation techniques of concern in March 2018.

In Charles Stross' 2013 science fiction novel, Neptune's Brood, the universal interstellar payment system is known as "bitcoin" and operates using cryptography.[227] 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."[228]
To be accepted by the rest of the network, a new block must contain a proof-of-work (PoW).[67] The system used is based on Adam Back's 1997 anti-spam scheme, Hashcash.[5][83] The PoW requires miners to find a number called a nonce, such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target.[3]:ch. 8 This proof is easy for any node in the network to verify, but extremely time-consuming to generate, as for a secure cryptographic hash, miners must try many different nonce values (usually the sequence of tested values is the ascending natural numbers: 0, 1, 2, 3, ...[3]:ch. 8) before meeting the difficulty target.

Once the recording of a transaction is on the Blockchain and the Blockchain has been updated, then the alteration of the records of this transaction is impossible. This is due to that particular transaction record being linked to the record of every preceding one. Blockchain records are permanent, they are ordered chronologically, and they are available to all the other nodes. The diagram shows an extract from the Bitcoin Blockchain.

RISK WARNING: Trading of and investing in cryptocurrencies and other investment products can carry a high level of risk, and may not be suitable for all investors. Trading and investing generally is not appropriate for someone with limited resources and limited investment or trading experience and low risk tolerance. You could sustain a total loss of your investment. Therefore, you should not speculate with capital that you cannot afford to lose. You should always understand that past performance is not necessarily indicative of future performance. Before trading and investing you should carefully consider your objectives, risk tolerance, financial resources, needs, your level of experience and other circumstances. Always seek advice from an independent financial advisor before making any trade or investment.
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. 
Investing in cryptocurrencies and Initial Coin Offerings ("ICOs") is highly risky and speculative, and this article is not a recommendation by Investopedia or the writer to invest in cryptocurrencies or ICOs. Since each individual's situation is unique, a qualified professional should always be consulted before making any financial decisions. Investopedia makes no representations or warranties as to the accuracy or timeliness of the information contained herein. As of the date this article was written, the author owns no crypto.
If you prefer to keep your bitcoins on your own computer, a desktop wallet is the wallet for you. A desktop wallet downloads and stores the entire blockchain. That means the wallet will have the entire ledger with every bitcoin transaction ever made. The size of the bitcoin blockchain is 30 gigabyte and growing, so keep that in mind, before going with a desktop wallet solution. The blockchain will take some time, maybe days to download, so you will not be able to deposit and withdraw bitcoins from the wallet until the whole blockchain has been downloaded. Also, everytime you start the wallet it needs to download all the latest transactions in the blockchain. You also need to make sure the wallet is backed up. Otherwise you will loose all your coins if your hard drive fails.
This timeless notion also applies to getting bitcoins. If you want to get a substantial amount of bitcoins fast, you need to spend money buying them. If you want to get a substantial amount of bitcoins for free, you need to spend a lot of time earning them on websites called bitcoin faucets.Expending monetary or mental resources to get bitcoins is a necessity. But some methods of buying and earning bitcoins are more effective than others. Read on to learn the best ways to buy bitcoins and the best ways to earn them for free through bitcoin faucets.
Rewards programs are a good use of cryptocurrencies, specifically tokens of the modern epoch, and one that might keep on giving is one that pays in Bitcoin. A network called BitcoinGet has a shopping service called CoinRebates which has a few major retailers including Walmart and Newegg within its network. You earn a varying amount of “bits” (100 satoshi = 1 bit) per dollar spent at each of the retailers. Walmart and others have in-store pickup, so you can effectively do your regular shopping and get a small Bitcoin rebate on it. Over time, this could really build up.
When the algorithm was created under the pseudonym Satoshi Nakamoto—which in Japanese is as common a name as Steve Smith—the individual(s) set a finite limit on the number of bitcoins that will ever exist: 21 million. Currently, more than 12 million are in circulation. That means that a little less than 9 million bitcoins are waiting to be discovered.

I can see that blockchain has at least one vulnerability. Sure – decentralization and reconciliation with encryption is fine. But the one vulnerability is the interconnecting network. You foul that up and your blockchain paradigm is now vulnerable. Each node could then be compromised so that reconciliation is impossible. Blockchain does not accomodate the vulnerabilities of the infrastructure which it is using.

Blockchain may make selling recorded music profitable again for artists by cutting out music companies and distributors like Apple or Spotify. The music you buy could even be encoded in the blockchain itself, making it a cloud archive for any song purchased. Because the amounts charged can be so small, subscription and streaming services will become irrelevant.
People need to understand that “blockchain” is NOT the same thing as “bitcoin”. Bitcoin was the first blockchain system designed, but there have been a number of others since then which are very different – they were designed by different people, often for different purposes. The ones moving into the business world today are NOT systems for electronic money. They are “ledger” systems that are used to replace existing methods, almost none of which are electronic money. Examples of such blockchain systems are Hyperledger (which has several different schemes, the most popular being Hyperledger Fabric), Ethereum, R3 Corda, and some others. They were NOT designed by “some guy” somewhere – they were designed by highly capable groups of people who are in the business of designing things for use by corporations to operate their businesses. Several of these are in open-source projects, where they are being developed jointly by many people, and are subject to study and analysis by all of them. There is work in early stages to define regional and international standards that will define some requirements for the blockchains. (I happen to be involved with some of those standards activities, as well as development on one of the blockchain systems.)
Transactions are defined using a Forth-like scripting language.[3]:ch. 5 Transactions consist of one or more inputs and one or more outputs. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output. To prevent double spending, each input must refer to a previous unspent output in the blockchain.[69] The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction. As in a cash transaction, the sum of inputs (coins used to pay) can exceed the intended sum of payments. In such a case, an additional output is used, returning the change back to the payer.[69] Any input satoshis not accounted for in the transaction outputs become the transaction fee.[69]