What did Qubic do to Monero in 2025?
In 2025, Qubic organized a large amount of computing power to mine Monero, then claimed it had gained enough control to carry out a 51% attack. The controversy was about control over Monero’s transaction history—not a break of its privacy protections—and Qubic’s claims were more sweeping than what outside observers could independently confirm.
What Qubic actually did
Qubic is a separate crypto project, not part of Monero. It directed participating miners toward Monero’s RandomX mining system, the calculation process that helps secure Monero and rewards miners with XMR.
Its approach also had an economic angle: mining Monero could generate revenue to support Qubic’s own token economy, including reported token buybacks and burns. A buyback purchases tokens from the market; a burn removes tokens from circulation.
As Qubic’s mining operation grew during 2025, it became a concern because too much mining power was being coordinated by one group. In August, Qubic publicly claimed majority control and presented its activity as a successful attack on Monero.
What a “51% attack” means here
Monero normally follows the valid chain of blocks with the most accumulated mining work. Blocks are batches of transactions, added roughly every two minutes.
If one coordinated group controls a majority of the mining power, it can potentially build an alternative transaction history faster than everyone else. That can let it:
- Replace recent blocks with its own blocks.
- Delay or exclude selected transactions.
- Reverse its own recent payments and try to spend those funds again.
Replacing recent blocks is called a chain reorganization, or reorg.
However, majority mining power does not let an attacker take coins from your wallet without your keys, create arbitrary extra XMR, or automatically reveal who sent a private transaction. Other network participants still check whether blocks follow Monero’s rules.
What was confirmed—and what remained disputed
There were reports of chain reorganizations and displaced blocks during the August controversy. Qubic claimed these demonstrated its ability to control the chain.
But you should separate three things: Qubic’s stated mining power, observed disruptions, and proof of sustained majority control. They are not interchangeable.
Mining power cannot be measured perfectly in real time. Public estimates rely partly on observed blocks and information supplied by mining pools—groups that combine miners’ computing power. Short periods of unusually successful mining can also distort estimates.
Independent observers disputed aspects of Qubic’s claims and how much control the group actually maintained. A reorg alone does not prove sustained majority control: smaller reorganizations can happen naturally, and some attacks can cause disruption without a lasting majority.
Why it mattered to you
The episode exposed a real risk: Monero’s privacy technology does not remove the danger of concentrated mining power.
If you were receiving XMR during suspected disruption, the practical concern was payment finality—how confident you could be that a payment would remain recorded. Waiting for more confirmations can reduce exposure, although no fixed wait guarantees safety against sustained majority control.
If you mine, including through a browser service, the relevant question is who ultimately controls the mining work your device contributes.
The bottom line
Qubic challenged Monero’s mining security in 2025 and claimed a successful majority attack. It did not thereby “crack Monero’s privacy.” The careful conclusion is that the episode raised serious mining-centralization concerns, while the claimed extent and duration of Qubic’s control remained disputed.
