Blockchain technology addresses security and reliability issues in a variety of ways. First, new blocks are always stored linearly and chronologically. That is, new blocks are always added "at the end" of the blockchain. If we look at Bitcoin's blockchain, you will see that each block has a position on the chain called "height". As of November’20, the block height had reached 656,197 blocks. Once a block has been added to the end of the blockchain, it is very difficult to go back and change the content of the block (unless the majority agree to do so). This is because each block contains its own hash, along with the hash of the previous block and the timestamp specified earlier. Hash codes are created by a mathematical operation that converts digital information into a sequence of numbers and letters. If this information is organized in any way, the hash code also changes. Let's say a hacker wants to change the blockchain and steal people's Bitcoins. If the hackers change their single copies, their system will no longer be compatible with anyone's copy. When everyone cross-references their copy, it is seen that this modified copy stands out and that this hacker's chain version is out of the system for being illegal. For such a hacking attempt to be successful, the hacker must be able to check and modify 51% of the copies of the blockchain at the same time. In this way, however, the modified copies constitute the majority and thus constitute an agreed chain. Simultaneously during such an attack, the hackers would have to redo all the blocks because only then would they have different timestamps and hash codes. An enormous amount of money and resources are needed for this process to be implemented. Given the size and growth rate of the Bitcoin network, the cost of achieving such a success will likely be insurmountable. Not only will this be very expensive, but will likely be fruitless. When network members see such drastic changes in the blockchain, it is useless to do such a thing because when network members become aware of the change, they will fork into a new, unaffected version of the chain. Such a development would cause the hacked version of Bitcoin to depreciate in value and the bad actor is in control of a worthless asset; After all, the attack becomes meaningless. The same thing happens again if the bad actor attacks Bitcoin's new fork. The system is built in this way so that people are encouraged to choose to participate in the network, as it is much more economical to take part in the network than attack it.