Qubic Claims 51% Control of Monero in Hashrate Battle
Update (Aug. 12, 2025, at 1:30 pm UTC): This article has been updated to add a Qubic announcement.
Layer-1 blockchain Qubic said it has “completed its attempt to dominate the Monero network,” claiming a month-long push culminated Monday with 51% control of Monero’s hashrate.
According to a Monday announcement, the “month-long, high-stakes technical confrontation” concluded with Qubic reaching 51% of Monero’s hashrate. The effort coincided with a six-block-deep chain reorganization that discarded 60 previously valid blocks, according to the Monero Consensus Status dashboard.
A six-block-deep reorganization is when the blockchain replaces the last six confirmed blocks with an alternate chain that is longer or has higher cumulative work. While Qubic said this shows that it carried out a succesful 51% attack on Monero, others are unconvinced by the claims.
The claim drew immediate pushback from developers who argued that the reorganization alone does not prove a successful 51% attack. SeraiDEX’s lead developer, Luke Parker, said in an X post that a six-block-deep network reorganization with block orphaning “does not mean a ‘51% attack’ was successful.”
“It does mean an adversary with a high amount of hash got lucky,” he added.
Related: 51% attack on Ethereum more difficult than on Bitcoin — Justin Drake
What is a 51% attack, and why is it important?
A 51% attack is when a single entity controls over half of a blockchain’s mining power or stake, allowing it to rewrite transactions or block them entirely. Zhong Chenming, the co-founder of crypto cybersecurity firm SlowMist, said in a Tuesday X post that “this time the 51% attack on Monero seems to have succeeded.” He added:
“The cost was also high, and it’s unclear what the economic benefits of doing this are in the end… In theory, the Qubic mining pool can now rewrite the blockchain, achieve double-spending, and censor any transactions.”
As of the time of writing, Monero’s price stood at about $247, down more than 8.6% from the price of over $276 reported 24 hours ago.
Related: Coin Metrics research shows BTC and ETH are immune to 51% attacks
How the confrontation unfolded
Qubic is a layer-1 blockchain that employs a “useful proof-of-work” model to route mining toward artificial intelligence tasks. Recently, the blockchain started routing part of its computing power to a malicious Monero (XMR) mining effort.
The Monero community noticed Qubic’s economic attack against Monero in late July. Monero’s community responded to the ongoing attack with its own countermeasures, including an alleged distributed denial-of-service attack against Qubic’s mining pool.
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