Security in Blockchain Technology

Blockchain technology is decentralized and trust-based in several ways. Initially, new blocks are always stored linearly and in chronological order; that is, they are always added to the end of the last block in the blockchain network.
Once a block is added to the end of the blockchain, it will be very difficult to go back to that block and change its contents unless the majority of the network nodes agree to do so; because each block contains its own hash and the hash of the previous block along with a timestamp. Hash codes are created by a mathematical function and convert digital information into a string of letters and numbers. If this information changes in any way, the hash code will also change.
Suppose a hacker running a node on the network intends to make changes to the blockchain and steal other people's digital currencies. If this person only changes his own node's blockchain version, the other nodes in the network will not be affected by it, and when other nodes match their versions, they will notice the difference in the hacker's version and that version will be removed from the system as "illegal" and invalid.
To succeed in such an attack, the hacker must simultaneously control 51% or more of the versions and change them so that the new versions are recognized as the majority and approved and agreed upon in the network. Carrying out such an attack requires a lot of hardware resources and money, since the processing of all blocks must be done again because these transactions require different time stamps and hash codes.
Given the size and speed of cryptocurrency networks, it would be impossible to estimate the cost of such a feat. Apart from being extremely expensive, this operation would also likely be fruitless. By doing this, the attention of other nodes will definitely be drawn to changes within the network.
In this case, the network members decide to create a hard fork, creating a new version of the blockchain with different features and rules for the network that does not have those changes. This process causes the price of that version of the cryptocurrency on the hacked blockchain to drop and completely neutralizes the attack, because the attacker has taken control of the worthless cryptocurrency network.
This happens again if the new version of the blockchain and cryptocurrency are attacked again. Given these circumstances, participating in the network is more profitable than attacking it. In a blockchain, you are a member of a network that only knows the members and you are sure that you are receiving accurate and correct information and that your confidential information on the blockchain is only shared with those to whom you have given permission to access.
Blockchain technology provides security and trust in the network in several ways. One of these is the automatic storage of blocks of information in a linear and chronological order. This means that the most recent block The block generated in a blockchain is always linked to the latest existing block, and after doing so, it is no longer possible to change previous blocks.
The nodes of each blockchain network operate on the basis of a consensus algorithm specific to that network. The consensus algorithm or mechanism, as the name suggests, defines the method of collective agreement among the network nodes to confirm transactions and blocks. Among the most well-known consensus algorithms are Proof of Work and Proof of Stake, which are specific to the world's leading blockchains, Bitcoin and Ethereum, respectively.
$BTC ‌$ETH ‌