Bitcoin Gold (BTG), a hard fork of the Bitcoin blockchain which uses the Equihash mining algorithm, has suffered a 51% attack.
The attack started on 18 May 2018, and saw an attacker with a considerable amount of hashing power steal a total of 388,201 BTG – valued at $18 million.
Thanks to their 51% hash power, the attacking miner was able to overwhelm honest miners on the blockchain and manipulate transactions to perform double-spend attacks.
A user who controls over 50% of the blockchain’s hashing power has the ability to do the following:
- Reverse transactions that they send while in control.
- Prevent some or all transactions from gaining confirmations.
- Prevent some or all other miners from mining valid blocks.
This type of attack allowed the attacker to easily target automated systems such as exchanges and manipulate the blockchain to steal BTG.
Following the attack, the Bitcoin Gold team announced it was monitoring the situation and was working to upgrade its proof of work consensus mechanism.