The privacy-focused cryptocurrency Monero suffered a suspected 51% attack on 12 Aug., after the Qubic mining pool said it had captured a majority of the network’s computing power. Blockchain security firm SlowMist reported a six-block chain reorganization consistent with a takeover, a finding echoed by external researchers. With more than half of Monero’s hashrate, Qubic can theoretically rewrite transaction history, execute double-spend transactions and censor payments. Ledger Chief Technology Officer Charles Guillemet estimated the operation could cost about $75 million a day, yet warned the dominance could remain profitable in the short term. Monero’s XMR token fell as much as 15% intraday to about $247, extending a month-long slide. Qubic described the move as an experiment intended to test Monero’s defences, but did not provide technical details. The incident ranks among the largest recorded 51% attacks on a major cryptocurrency and has renewed scrutiny of the security of proof-of-work privacy coins.