So if I read this correctly… monero has suffered a 51% attack (this year). Bitcoin has not. Is it that crazy for a lunatic to question whether monero is “decentralized enough”?
Discussion
What happend, tell me more.
The major incidents:
18‑block chain reorganization (September 14, 2025)
A mining pool called Qubic gained over 50% of Monero’s hash rate and executed an 18‑block reorg, reversing 117–118 transactions.
This was the largest reorg in Monero’s history.
Previous 6‑block reorg (August 2025)
Qubic had already performed a six‑block reorg after accumulating majority hash power.
Impact on users
Merchants and exchanges saw confirmed transactions disappear, and payments that appeared final were invalidated.
No cryptographic break
Importantly, no funds were stolen, and Monero’s privacy features (RingCT, stealth addresses, etc.) were not broken.
The compromise was about network control, not cryptography.
Do your research. At peak Qubic had about 37% hashrate and performed what's called a selfish mining attack. All PoW coins are susceptible to this including Bitcoin. There were numerous 9 block reorgs (just below the 10 block confirmation requirement for finality) so there caused major delays in transaction timing but no finality was broken.
There was once a 18 block reorg which was clearly a major fuckup on Qubics part as come from beyond was in denial of it on X and was playing damage control. Off of memory about 100 or so transactions were invalidated and stuck in mempool for a week. Those could have been double spent against merchants thus the severity of the reorg. Only 10 and beyond block reorgs are damaging to finality though. Nobody reported double spends but it surely was possible at this one incident. Once again you don't need 51% for this attack, it's a selfish mining attack so Qubic got on a lucky streak, outmined the other pools in secret, then dumped their new longer chain on the network.
If they got 51% they could create true on-chain double spends, isolate miners and create permanant dominance over the chain. That attack is entirely different from the selfish mining attack we saw and would have resulted in permanent damage to the network.
Assume that’s true, how did the reorg of the chain happen with less hash power? That’s actually a worse than a 51% attack. No?
good news. today you will finally learn what selfish mining is
It's a side effect of PoW which is probabilistic thats why you have to wait for confirmations. They can happen unintentionally. You don't need a majority of hash power for a reorg to happen either. Though the more hash power an entity has the more likely it happens.
Forgot to add Qubic was definitely intentional reorgs though. They did it for brief periods with significantly less than 51% of hash power. Same selfish mining attacks can be done with just about any PoW coin. It's an economic attack. Miners are incentivized to switch because they will get the the reward from the native coin + the attacking coin reward. It will always be worth more to do that than mining natively. There are several ways to greatly mitigate this though. Like variations of workshare schemes for example which is what Monero is in the process of implementing.