August 11, 2025: the pool linked to Qubic has surpassed the critical threshold in some operational windows on Monero, reaching 63 blocks out of 122 and causing a reorganization (reorg) of up to 6 blocks.
Following the event, some exchanges – including Kraken – have prudently suspended deposits in XMR, while the community has accelerated the migration towards P2Pool.
For details of the event in the media and for the technical context, see also the journalistic reconstruction and the literature on the phenomenon of selfish mining: the academic reference study on the subject Eyal & Sirer (2014).
According to the data collected by our on‑chain monitors and public dashboards (for example xmrchain and MoneroBlocks), in critical windows the pool reached a hashrate share consistent with 51.6% calculated over the 122 block window.
We have verified dozens of orphan blocks and multiple reorgs up to 6 blocks; the same indicators show that the pressure on hashpower allocation was concentrated in discontinuous intervals rather than continuous. Data updated as of August 27, 2025.
What happened, in brief
- 51% threshold exceeded: in certain operational windows, the Qubic pool concentrated the majority of the hashrate and published a private chain to the detriment of the main network.
- Deep reorganizations: up to 6 blocks replaced, with dozens of blocks left orphaned (stale).
- Immediate impact: deposits in XMR suspended or slowed down on various exchanges and increase in confirmation requirements.
- Economic dynamics: external incentives through buyback & burn of QUBIC have channeled a significant share of hashpower to Monero.
- Spillover risk: the Qubic community has already indicated the intention to focus, in a subsequent phase, on Dogecoin – a PoW network with, according to updated market data, a market capitalization of about 35 billion dollars as of August 27, 2025.
Who is Qubic and why its incentive shifted the hashrate
Qubic is a Layer‑1 chain founded by Sergey Ivancheglo, known for his role in the IOTA ecosystem. The project adopts a Proof of Useful Work that, in addition to traditional PoW, directs computing power towards “useful” tasks – for example, processing artificial intelligence algorithms.
The focus is the economic model: with the buyback & burn mechanism, Qubic incentivizes mining on third-party networks. In practice:
- The miners extract XMR on Monero and receive the usual rewards.
- The rewards in XMR are converted into USDT on the market.
- With these funds, tokens QUBIC are purchased, which are partly burned and partly redistributed as a bonus.
The result is twofold: on one hand, it creates deflationary pressure on the QUBIC token; on the other, it offers an expected return for pool participants potentially higher than that obtainable with direct mining on Monero.
Not surprisingly, many CPU‑miners have recently focused their hashrate precisely on the Qubic pool. It must be said that the network’s response has moved in parallel.
Chronology of the escalation
Essential Timeline
- May 2023: the contribution of the Qubic pool to Monero mining was marginal, below 2%.
- End of July 2025: the pool’s share exceeds 25%, with peaks among the main players in the pool landscape.
- August 11, 2025: Qubic claims operational windows with over 51% of the hashrate, applying selfish mining practices; in a window of 122 blocks, the pool produces 63.
Key Numbers
- 63/122 blocks produced in a critical window (approximately 51.6%).
- Reorganization of up to 6 blocks into individual events, resulting in the formation of orphan blocks.
- High concentration of hashrate on a single pool in specific time windows.
How a 51% attack works
Selfish mining, in simple words
With control over more than 51% of the hashrate, an actor can withhold newly found blocks by building a private chain. When it is advantageous, the private chain is published and turns out to be longer than the public one, triggering the reordering of the latest confirmations.
In this way, some transactions can be excluded (censorship) or attempts at double spending can be made. In this context, the timing and strategy of publication make the difference.
Censorship and centralization: the risks
- Selective censorship: some payments or transactions might be deliberately omitted.
- Slower confirmations: in reaction to the attack, the exchange have increased the number of confirmations required to process transactions.
- Structural fragility: a high concentration of hashpower in a few pools reduces the overall resilience of the network.
Practical impact on users, merchants, and exchanges
- Double spending: transactions already confirmed can be “rewritten” following the reorg.
- Stale blocks: the increase in orphan blocks leads to an accumulation of pending transactions in the mempool.
- Suspended or delayed deposits: in response to the attack, some platforms – as confirmed by Kraken – have temporarily suspended deposits in XMR.
The Qubic team admitted to using selfish mining techniques and operational windows in which their pool held over 51% of the hashrate. The episode prompted operators and infrastructures to tighten risk policies. An interesting aspect is the speed with which such measures were adopted.
Why the buyback & burn made the difference
- Price and narrative: the purchase and burning operations of the tokens create a narrative of scarcity, capable of influencing the market value of the token.
- Expected return: between bonus and potential appreciation of the QUBIC, the return for pool participants can exceed that of native mining.
- Network effect: the entry of more miners increases the probability of producing blocks within the pool, fueling the cycle of incentives.
In essence, a well-structured external economic incentive can impact the security of a third-party PoW network, opening windows of vulnerability without the attacker having to invest in hardware dedicated to that specific network. It should be noted that not all networks react in the same way.
Community reactions and regulatory debate
The Monero community has moved on multiple fronts. On one hand, there has been an increase in migration towards decentralized mining solutions like P2Pool to strengthen the distribution of the hashrate; on the other hand, “contextual” measures have been adopted such as raising the number of confirmations required by exchanges and initiating discussions on possible consensus mitigations. Some developers have reiterated that a deep reorg does not prove a permanent control of the hashrate, but rather a period of predominance.
There are also unverified estimates suggesting that maintaining total and prolonged control would require investments on the order of tens of millions of dollars per day, a point discussed at the risk analysis level.
The economic sustainability of a continuous attack thus remains a subject of debate and strongly depends on market dynamics, the liquidity of exchanges, and the conversion costs of the incentivizing token.
In parallel, the episode reignites the regulatory debate on privacy coin and the growing concentration of pools, fueling demands for greater operational transparency and, in some circles, for reforms aimed at promoting a wider distribution of hashrate.
Dogecoin in the spotlight: risk of inter-chain contagion
The Qubic community has expressed the intention to direct its efforts towards Dogecoin, a PoW network whose capitalization, according to the data reported by CoinMarketCap, currently exceeds 35 billion dollars as of August 27, 2025.
If the “buyback & burn” approach and the concentration of hashrate were replicated, even networks with merge-mining or consolidated pool structures could face similar pressures. The message to the market is clear: token-incentives can become economic tools capable of influencing entire blockchain.
Realistic countermeasures for PoW networks
- Decentralized pools: encourage and adopt solutions like P2Pool to reduce the risk of a single point of concentration.
- Consensus parameters: evaluate temporary adjustments of the consensus parameters to disincentivize opportunistic hashrate coming from external sources.
- Risk policy: increase confirmations for particularly sensitive transactions and promote coordination between exchanges, pools, and developers.
- On-chain monitoring: implement alert systems to observe the distribution of hashrate, any reorgs, and abnormal rates of stale blocks; public dashboards like xmrchain assist collaborative monitoring.
Why this story matters
The Qubic–Monero case shows how the security of a PoW blockchain does not depend solely on hardware, but also on economic incentives and pool governance.
It is a change of perspective where “off-chain” remuneration models can, in certain windows, allow operational control over third-party networks. That said, the response capability of the community remains a decisive factor.
Editorial note: for some technical details – such as specific reorg logs and complete official statements from the Qubic team – further primary references are needed. We have linked dashboards and public sources; additional updates will be integrated as soon as they are available. Data updated as of August 27, 2025.
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