Blockchain appeared the exact time is no relevant information, even its "initiator" Satoshi Nakamoto also do not know who.

Since 2009, as more and more people participated, blockchain 1.0, represented by Bitcoin, was finally formed. In 2013, Vitalik Buterin was inspired by Bitcoin and proposed the Ethereum blockchain smart contract platform, which officially opened the ICO model.

So ICOs aren't new, they're just popping up in the world of ordinary people. On Ethereum, anyone can quickly create their own token, and the threshold for an ICO is so low that it only takes a tear of a white paper.

Ethereum's most important feature compared to Bitcoin's network is its support for smart contracts. This makes the blockchain more imaginative, not just a network of ledgers for bookkeeping, but a richer scenario.

To put it simply, smart contracts are divided into three parts: an input, an output, and an execution condition. It is stored on the blockchain and is approved by the parties involved.

Our normal application software can be simply viewed as these three parts, we input through the action, the software output through the screen, some internal conditional execution. It's just that on blockchain, it's all simplified.

Here, incidentally, is the notion of Turing completeness. That is, all functions of Turing machine can be satisfied without considering hardware constraints.

Smart contracts are Turing complete, that is to say, we can now run on mobile phones, computer programs can be done with smart contracts, but due to the blockchain performance constraints, cannot run. This may also explain why some bigwigs say that blockchain can be the next generation of the Internet.

However, smart contract also has an Achilles heel: based on the characteristics of blockchain, it cannot be tampered with. In case the smart contract is released with a bug, it is really useless, and we have to make a new one.

The blockchain is not completely secure: in theory, if a hacker had control of 51% of the nodes, he could do whatever he wanted. In addition, the blockchain fork is also risky, anyone can initiate a fork, then can launch a replay attack.

For example, BTC forks into a BCC. Before the fork, both chains accept the transaction, but after the fork, it is different. So before the fork, you can spend it once on BTC, you can spend it once on BCC. So the general exchange does not support forking

In addition, the most important private key in the blockchain is also vulnerable to theft and almost irreparable. The way to steal the private key is very simple, through traditional Trojan viruses, phishing sites and the like can be stolen. And if it's stolen, there's no centralized organization looking out for your rights. You have to take it all on yourself.