Although Monero has long been regarded as a bastion of privacy and decentralization within the cryptocurrency landscape, recent developments have cast a spotlight on vulnerabilities in its mining ecosystem, as Qubic—a mining operation—asserted control over more than 51% of Monero’s total hashrate by August 2025. Attaining this majority threshold, Qubic theoretically gained the capability to manipulate the blockchain through block reorganization, transaction censorship, and potential double-spend attacks, activities that fundamentally threaten the integrity of the network’s consensus mechanism. This incident resulted in the reorganization of multiple blocks and the creation of numerous orphan blocks, underscoring the tangible effects of such centralization risks on Monero’s blockchain. Such scenarios highlight the importance of resilient consensus protocols like GHOSTDAG that weave parallel blocks to enhance security.
Qubic’s ascent was remarkably swift, with its share of the hashrate climbing from under 2% in May to over 25% by late July, before surpassing the critical 51% mark shortly thereafter. This rapid accumulation sparked widespread concern across the Monero community and broader cryptocurrency markets, reflected in an immediate price decline of approximately 6 to 7 percent within 24 hours of the announcement. Such a market reaction underscored the perceived risk posed by a potential “51% attack,” a security vulnerability rare in large, decentralized networks but particularly consequential for privacy-centric cryptocurrencies reliant on robust consensus. Kraken’s decision to pause Monero deposits highlighted growing industry caution in response to the risks posed by such a proof-of-work vulnerability.
Qubic’s swift rise to 51% hashrate triggered market fears of a rare and dangerous 51% attack.
The economic and strategic motivations behind Qubic’s mining dominance are rooted in its “useful proof-of-work” model, wherein mining rewards are converted into stablecoins to repurchase and burn QUBIC tokens, creating direct economic incentives for miners. This strategy, articulated by Sergey Ivancheglo, Qubic’s founder and co-founder of IOTA, frames the operation as a deliberate stress test designed to prepare the Monero ecosystem for adversarial scenarios. The approach integrates AI applications with cryptocurrency mining, promoting “real market value” generation while employing tactics akin to selfish mining to maintain blockchain control.
In response, major exchanges such as Kraken temporarily suspended Monero deposits to mitigate risks related to blockchain reorganizations and double-spends, while community actors reportedly launched distributed denial-of-service attacks targeting Qubic’s infrastructure. Although these countermeasures disrupted Qubic’s dominance temporarily, the mining pool regained some hashrate control, prompting ongoing scrutiny of Monero’s decentralization and mining pool resilience. The incident exposes underlying challenges in Monero’s proof-of-work security assumptions, raising critical questions about the robustness of privacy-focused blockchains against economically motivated centralization pressures.
