Qubic Claims 51% Control of Monero Network Sparking Security Fears

Qubic, a mining pool led by IOTA co-founder Sergey Ivancheglo, has claimed control of over 51% of Monero’s hashrate, triggering widespread concerns about network security and potential blockchain reorganization risks. This development has prompted warnings from the Monero core team and developers, who have advised users to increase transaction confirmation thresholds and temporarily pause transactions to mitigate the impact of potential chain instability [1]. According to Ivancheglo, the move is part of a planned technical test to study network security dynamics, though the implications have been interpreted as more concerning by many in the community [2].

Reports indicate that Qubic executed a six-block deep reorganization, a move that heightened fears of double-spending, censorship, and transaction manipulation [3]. The mining pool’s control was facilitated by the "useful proof-of-work" (uPoW) mechanism, which allows hashing power to be reused across multiple blockchains. This technical advantage enabled Qubic to rapidly gain dominance over Monero’s decentralized network, temporarily rejecting blocks from other mining pools [4].

In response, exchanges such as Binance have paused XMR deposits to protect users from potential reorg-related vulnerabilities, while Monero developers have urged the community to adopt more stringent confirmation requirements [5]. Some community members have also proposed strategies to counter the centralization risk, including incentives for smaller miners to increase hashrate distribution and improve network decentralization [6].

Despite Qubic’s claim that the activity was a “technical demonstration,” experts have warned that the event highlights significant vulnerabilities in Monero’s consensus model. The incident has also raised broader questions about the security of smaller proof-of-work blockchains, which may struggle to maintain decentralization when faced with mining pool concentration [7].

Monero’s price has since fallen to a three-month low, reflecting investor concerns over the risks of transaction insecurity and double-spending. Analysts warn that a sustained 51% attack could undermine confidence in Monero, particularly given its reputation as a privacy-focused cryptocurrency [8]. While the attack appears to have been temporary, the incident serves as a stark reminder of the fragility of blockchain networks when hashrate distribution is uneven [9].

As the Monero community continues to monitor the situation, the broader crypto market is also watching closely. The incident underscores the risks associated with uPoW mechanisms and the importance of maintaining a balanced and decentralized hashrate structure to prevent future attacks.

Sources:

[1] Theblock.co (https://www.theblock.co/post/366535/monero-faces-chain-reorganization-fears-after-qubic-says-it-controls-51-of-hashrate)

[2] CoinMarketCap (https://coinmarketcap.com/community/articles/689b3d1ae5de8d42b785ed97/)

[3] Bitget.com (https://www.bitget.com/news/detail/12560604907938)

[4] Binance.com (https://www.binance.com/en/square/post/28212728588970)

[5] Gate.com (https://www.gate.com/post/status/12977558)

[6] CryptoRank.io (https://cryptorank.io/news/feed/5c94e-qubic-mining-pool-takes-over-monero-network-in-major-51-attack)

[7] Gate.com (https://www.gate.com/post/status/12978260)

[8] Coinpedia.org (https://coinpedia.org/news/monero-faces-major-51-attack-threat-xmr-price-slides-to-3-month-low/)

[9] Mitrade.com (https://www.mitrade.com/au/insights/news/live-news/article-3-1032606-20250812)