Qubic Claims Majority Control of Monero Hashrate, Raising 51% Attack Fears

Qubic, a project led by former IOTA co-founder Sergey Ivancheglo, says it has secured more than 51% of Monero’s global hashrate, a milestone that, if true, gives it the ability to reorganize blocks, censor transactions, and attempt double-spends on the privacy-focused blockchain.

Ivancheglo framed the move as a stress test to help the Monero community prepare for future network threats, but the announcement has triggered sharp debate among developers and security experts.

A 51% attack occurs when a single entity or coordinated group controls a majority of a proof-of-work network’s hashrate. Ethereum Classic suffered multiple reorganizations in 2020, resulting in millions of dollars in losses, while Bitcoin Gold faced similar assaults in 2018 and 2020.

Smaller networks like Verge have also been targeted, demonstrating how concentrated hashing power can destabilize and entire cryptocurrency network.

Monero, which uses the CPU-friendly RandomX algorithm, has long prided itself on resisting ASIC centralization. Qubic’s “useful proof-of-work” (uPoW) model repurposes Monero mining rewards by converting $XMR into USDT, then using the proceeds to buy and burn QUBIC tokens, a deflationary mechanism that doubles as a liquidity sink for its own ecosystem.

From mid-May to late July, Qubic’s share of the network jumped from less than 2% to over 25%, at times topping pool rankings.

Ledger CTO Charles Guillemet warned on X that Monero “appears to be in the midst of a successful 51% attack,” citing signs of a major chain reorganization, with several other industry experts like SlowMist founder Yu Xian expressing their doubt over Qubic’s economics.

Whether the events mark a hostile takeover or simply a stress test, $XMR has responded negatively, dropping by 6.65% in the past 24 hours to compound a 16% decline over the past week.

Read more: How $330M BTC Hacker May Have Doubled Down on Monero Derivatives