- Qubic amassed a majority of Monero hashrate and a major chain reorganization was observed.
- The pool later said it paused the attack as XMR fell about 13 percent.
Monero experienced a significant chain reorganization after the Qubic mining pool concentrated a majority share of network hashrate. Public posts stated that the pool could influence block ordering and transaction inclusion as the event unfolded.
Major chain reorganization detected as Qubic concentrates hashrate
The privacy focused network launched in 2014 has long faced pressure from regulators and major exchanges. A majority hashrate position enables a coordinating miner to rewrite recent blocks, execute double spending and censor transactions.
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With such dominance a miner can orphan competing blocks, leaving other participants with little incentive to continue mining because expected rewards diminish when competing work is discarded.
Observers contrasted the scale of resources involved by noting that a chain with an estimated market value near three hundred million dollars appeared to be challenging a network valued near six billion dollars.
During the disruption Monero’s XMR token declined by roughly thirteen percent. The market move reflected uncertainty about the duration and intensity of the pressure on consensus rather than a definitive assessment of long term utility.
Monero appears to be in the midst of a successful 51% attack.
The privacy-focused blockchain, launched in 2014 and long targeted by governments and 3-letters agencies, is already banned from most major centralized exchanges.
The Qubic mining pool has been amassing hashrate for…
— Charles Guillemet (@P3b7_) August 12, 2025
Cost estimates varied. Some commentary put a full scale sustained takeover in the range of seventy five million dollars per day if built on dedicated hardware and continuous operation.
Other assessments argued that ongoing expenditure could be closer to one hundred thousand dollars per day if the required compute is rented for short periods, while acknowledging that capital costs for a long lived footprint would be materially higher.
Analysts also reiterated that a profitable selfish mining reorganization can be attempted with roughly one third of network power, while persistent control over block production requires a majority share of hashrate.
Qubic states temporary halt and disables API during reorganization
Shortly after the reorganization began Qubic said it had chosen not to take over Monero at that time and indicated that the selfish mining activity had been paused.
During the episode the pool’s public API was reportedly disabled, which complicated independent assessments of its effective hashrate and the precise extent of the reorg.
The stated pause left open questions about whether the operation sought to demonstrate capability, to pursue double spend opportunities, or to test market and community responses.
For Monero the immediate risk centers on the incentive structure for honest miners. If one actor can repeatedly reorganize blocks and orphan rivals, the expected return for independent miners falls and network security can erode as they power down.
Community options are constrained in the near term and may include coordinating temporary defenses, evaluating protocol level changes to proof of work parameters, or encouraging greater hashrate diversity across pools.
The episode underscores how concentrated compute can enable reorganizations even when full consensus capture is not continuously maintained.
At the time of this update, Monero (XMR) is trading at $253.75, reflecting a decline of exactly $5.12, or −1.98% compared to the previous close.
