Attack or Stress Test?
In August, Monero (XMR) endured one of its most severe challenges when Qubic, a mining pool founded by former IOTA co-founder Sergey Ivancheglo, claimed majority control of the network’s hashrate. CoinDesk reported that Qubic triggered several reorganizations of the blockchain, raising questions about whether the event constituted a full 51% attack or a temporary stress test.
Security firm Halborn described the incident as a “clear example of selfish mining,” where a dominant miner can rewrite blocks and destabilize consensus. “A six-block reorg doesn’t guarantee total chain capture,” Halborn explained, “but it proves that concentrated hashrate can seriously disrupt trust, even on networks long considered resilient.”
The market reacted sharply. AInvest noted that Monero’s price fell about 16 percent during the week of the attack, sliding to roughly $250. For a privacy coin often seen as insulated from market swings, the sell-off underscored the severity of investor concern.
Exchanges React
Centralized platforms moved quickly to contain risk. CoinTelegraph reported that Kraken paused Monero deposits in the hours following Qubic’s claim. When services resumed, deposits required 720 confirmations, effectively forcing users to wait almost a full day before funds cleared.
Riccardo “Fluffypony” Spagni, Monero’s former lead maintainer, called the exchange response “inevitable but troubling,” emphasizing that higher confirmation requirements restrict liquidity and erode user confidence.
Consensus Solutions
In the aftermath, Monero developers began debating long-term fixes. CoinCentral highlighted discussions about integrating Dash’s ChainLocks, which use validator signatures to prevent deep reorganizations. Spagni also pointed to an experimental technique called “detective mining,” which aims to detect selfish mining in real time.
Luke Parker, a Monero researcher, argued that the episode showed the need for hybrid defenses. “We don’t need to reinvent proof-of-work,” Parker said, “but we do need to layer protections so that even a majority pool can’t quietly rewrite history.”
PoW Lessons Learned
The Monero scare revealed deep fault lines in the proof-of-work model. ForkLog described the incident as a reminder that mid-cap PoW coins remain vulnerable if mining power becomes concentrated, unlike Bitcoin’s vast and diversified hashrate. The debate over whether this was truly a 51% attack or simply a reorg highlighted the ambiguity that surrounds PoW’s security guarantees.
For some, the event underscored resilience—Monero stabilized, and no confirmed double-spends occurred. For others, it exposed fragility, since a single pool demonstrated the ability to destabilize a major privacy network and spook exchanges and investors.
Looking Ahead
Developers are preparing technical audits of Qubic’s claim and will update the community on whether ChainLocks or detective mining will be pursued. Exchanges are reassessing confirmation thresholds, and the broader debate over proof-of-work resilience continues, especially for privacy-focused tokens that rely on smaller but passionate mining communities.
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