Monero (XMR) has once again faced a 51% attack scare. An 18-block reorganization was confirmed on the network, raising concerns about the cryptocurrency’s long-standing reputation for privacy and decentralization.
The event was first flagged by community observer @OrangeFren Users were advised to extend their confirmation windows, with warnings that the usual 10 confirmations may no longer be sufficient.
SlowMist founder @evilcos compared the situation to a “Damocles’ sword” hanging over the ecosystem. He noted that ignoring reorg risks could leave the community vulnerable to double-spending attempts.
The Impacted Blocks
The reorg spanned blocks 3499659 through 3499676, wiping out a large batch of recent transactions. According to blockchain data, a “massive amount” of transactions became invalidated, forcing participants to resubmit and wait for inclusion in later blocks.
https://twitter.com/vinibarbosabr/status/1967202524810584454?t=TAZo490VG-QhRdPW0nTpvA&s=19
Community member described the incident as a form of selfish mining attack, where malicious actors reorganize blocks to maximize profits at the expense of the network’s stability.
For some, the damage was enough to lose faith. Barbosa himself announced:
“Personally, I don’t consider the Monero network reliable at this point. I’ll stop accepting $XMR for payments until this situation is resolved.”
A Surge in Orphan Blocks
The disruption did not end with the reorg. In the past 720 blocks (~24 hours), Monero has seen 213 blocks orphaned, a figure representing 29.5% of total blocks produced in that window.
Of these, 114 orphan blocks came from known pools, while 99 blocks were mined by unknown pools or solo miners. This near 30% orphan rate is 10x to 30x higher than historical norms.
To put it in perspective:
- Normal orphan rate in PoW is 1–3%.
- Even during the “Qubic” incident weeks ago, the peak reached 60/720 (8.3%).
- More recent disruptions saw 48/720 (6.7%) orphans.
Today’s 213/720 stands far above those thresholds.
Why Orphan Blocks Matter
In Proof-of-Work (PoW) systems, orphan blocks occur when two miners discover valid blocks nearly simultaneously. The network eventually discards one of them, leaving transactions inside the orphaned block unconfirmed.
Usually, this is rare and manageable. But with nearly 30% of Monero’s blocks orphaned, the issue becomes systemic. Transactions risk being delayed, invalidated, or requiring repeated submissions.
That threatens Monero’s basic user experience and reliability, especially for those using XMR in commerce. The traditional 10 confirmations are no longer a reliable safeguard. Users may need to wait significantly longer to trust finality.
Qubic’s Role: Selfish Mining Tactics
Analysis points to Qubic, a competing mining protocol, as the actor behind these disturbances. Qubic miners appear to be employing a selfish mining strategy involving:
- Silent mining: hiding hashrate from other nodes
- Deep reorganizations: causing chain instability
- Empty blocks: mining without transactions to maximize personal gains
These tactics disrupt Monero’s consensus, even without achieving a full-blown 51% attack.
The Economics of the Attack
The economic logic driving this attack is complex but compelling.
- Estimated cost: Around $75 million per day to sustain the attack
- Profitability: Mining via Qubic yields 3x the profit compared to mining Monero directly
- Buyback system: Profits generated are funneled back into buying and burning QUBIC tokens
This creates a self-reinforcing cycle, the more disruption caused, the more valuable QUBIC’s token becomes through buybacks, incentivizing continued attacks.
Network Reliability at Stake
Monero has long prided itself on privacy, censorship resistance, and reliability. But this recent 18-block reorg, paired with the staggering orphan block rate, challenges that reputation.
The event does not necessarily mean double spending has occurred. But it undermines confidence in Monero’s transaction confirmation model. If users can no longer rely on 10 confirmations, the risk profile of using XMR in commerce increases dramatically.
https://twitter.com/liberlion17/status/1967183827828412701?t=TAZo490VG-QhRdPW0nTpvA&s=19
Historical Context
Looking back, Monero has endured unusual orphan block spikes before. For example:
- August: 5/720 orphans triggered warnings
- Qubic peak: 60/720 (8.3%) set records
- Two weeks ago: 48/720 (6.7%) windows raised alarms
But today’s 213/720 (29.5%) eclipses them all, signaling an extraordinary anomaly in Monero’s chain history.
The recent events reveal a chilling reality: Monero may not need to suffer a textbook 51% attack to feel its impact. Continuous deep reorganizations and an abnormally high orphan block rate erode trust in the network.
Transactions risk remaining stuck, invalid, or delayed. Merchants may withdraw XMR support. And users may demand far longer confirmation times to avoid losses.
For now, Monero’s community faces a difficult question: Can the network withstand continuous selfish mining without fundamental changes?
The Damocles’ sword remains hanging.
Disclosure: This is not trading or investment advice. Always do your research before buying any cryptocurrency or investing in any services.
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