51% Attack

What is 51% Attack?

A 51% attack occurs when a person or group gains control of more than half of a blockchain’s mining power or staked tokens. With this majority control, the attacker can influence block creation and potentially reverse their own transactions.

How does 51% Attack work?

1. The attacker gains control of over 50% of network power.
2. They produce blocks faster than the rest of the network.
3. The attacker builds a longer chain than the honest network.
4. The network accepts the longest chain as valid.
5. Previous transactions may be reversed, enabling double-spending.

Why does 51% Attack matter?

This attack threatens blockchain security by allowing transaction reversal and double-spending. Large networks like Bitcoin are highly resistant because controlling most of the network power would be extremely expensive.

Key features of 51% Attack

• Requires majority network control
• Can reverse transactions
• Enables double-spending
• More feasible on smaller networks
• Extremely costly on large blockchains

Examples of 51% Attack

Some smaller cryptocurrencies, such as Ethereum Classic and Bitcoin Gold, have experienced 51% attacks, where attackers reorganized blocks and double-spent funds.