Bitcoin Gold Blockchain Hit by 51% Attack Leading to $70K Double Spend

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The Bitcoin Gold blockchain has suffered a 51% attack resulting in over $70,000 worth of BTG being double spent.

According to a GitHub post by James Lovejoy, a researcher at MIT's Digital Currency Initiative, the hard-fork of Bitcoin was hit by two deep reorganizations of over 10 blocks on Jan. 23 and 24.

A 51% attack is a situation where a single entity or group controls over half of the hashpower securing a blockchain.

In the first attack, just after 18:00 GMT on Jan. 23, 14 blocks were removed from the blockchain and 13 then added.

Just over six hours later, in the early hours of Jan. 24, another attack removed 15 blocks and added 16.

Based on Nicehash market prices for Zhash, the estimated cost of each blockchain reorganization attack was around $1,700.

The attacker would have recouped around the same value in block rewards, meaning that the attacks at least broke even, and were possibly profitable if the double spend was successfully extracted from the system.

Following the attack, the price of Bitcoin Gold spiked.

Binance has since increased its withdrawal requirement to 20 blocks, although this still does not preclude the possibility of a 51% attack being financially viable.

As Cointelegraph reported, Bitcoin Gold was previously the subject of a 51% attack back in May 2018, when an estimated $18 million of BTG was overspent, leading to the coin being delisted on Bittrex.