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Firo is latest proof-of-work coin to suffer 51% attack; 306 blocks rolled back

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Privacy-focused digital currency, Firo, formerly known as Zcoin, suffered a 51% attack in the early hours of 20 January. Taking to Twitter, the team behind Firo notified traders about the attack and asked users not to make transactions until the network returned to a normal state. 

At the same time, CEO of Binance, Changpeng Zhao (CZ) stated that the miner behind the attack rolled back 306 blocks, which stopped on-chain transactions at the time:

Firo team further added: 

We will post updates when we have them. Note this is not a coding error but a nature of PoW.

The Firo project is a Proof-of-Work (PoW) blockchain, and such projects tend to be prone to 51% reorgs, especially when a small to medium scale protocol is involved.  

Previously, PoW blockchains such as Ethereum Classic, were attacked which resulted in the reorganization of over 7,000 blocks that corresponded to about two days of mining. Other PoW chains such as BCHA and Grin – which is also a privacy coin – suffered 51% attacks as well.  

Firo’s Co-Founder and Project Steward, Reuben Yap said in a report that the attack was stopped. Yap revealed that Firo was still working with exchanges to resolve the matter.

Exchanges are the ones at a loss as the attacker had deposited funds which have now been reversed because of the 51% attack…From what we know at the moment both Binance and Indodax were affected.

Firo is reportedly probing into the motives behind the attack as they are suspicious about the timing of the incident, which took place when they were close to deploying chainlocks. According to the Firo team, a feature on the blockchain called Chainlocks that mitigates such attacks was being tested on Firo’s testnet and was apparently “weeks away from deployment.”


Alisha is a full-time journalist at AMBCrypto. Her interests lie in blockchain technology, crypto-crimes, and market developments in Africa and the United States
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