Answer:
4-Hackers gaining access to more than 50% of the network's mining power.
Step-by-step explanation:
Hackers gaining control of more than 50% of a blockchain network's mining power is known as a 51% attack and is a significant security threat to blockchain systems. In a blockchain, mining power refers to the computational power and resources used to validate transactions and add new blocks to the chain.
If a malicious entity or a group of hackers controls the majority of the network's mining power, they can potentially manipulate the blockchain's consensus mechanism. They could perform double-spending attacks, reverse transactions, exclude certain transactions from being included in blocks, or rewrite the entire blockchain history.
This type of attack undermines the decentralized nature and security guarantees of blockchain systems. It highlights the importance of maintaining a distributed network and ensuring that no single entity or group can control the majority of the mining power. Various consensus mechanisms and security measures are implemented in blockchain networks to mitigate the risk of such attacks.