Questions » What is a reorg?

What is a reorg?

In the context of cryptocurrencies, a reorg or a blockchain reorganization refers to a situation where a blockchain network’s history is rewritten, typically due to a chain split caused by a fork or a 51% attack.

A reorg happens when a different chain becomes the longest and therefore the valid chain in the network, and nodes switch to the new chain to maintain consensus. The reorg can result in transactions being reversed or orphaned, meaning they are no longer valid and need to be re-sent.

Reorgs can occur for several reasons, including a software bug, a hard fork, a 51% attack, or a network upgrade. In the case of a 51% attack, the attacker can use their computing power to mine a longer chain fork than the legitimate chain, causing the network to switch to the new chain and potentially reverse transactions.

Reorgs can have significant implications for the security and stability of a blockchain network. In the case of a malicious attack, a reorg can cause distrust in the network, as users may question the integrity of the blockchain. However, in most cases, reorgs are a necessary part of the decentralized consensus mechanism and are often resolved quickly by the network.