Qubic's bid for 51% of Monero's hashrate sparks controversy

Privacy-focused network Monero is grappling with a potential network takeover attempt by Qubic, a blockchain project led by IOTA co-founder Sergey Ivancheglo, otherwise known as CFB.

Qubic uses a novel "useful proof-of-work" (uPoW) system that has been incentivizing Monero CPU mining to fuel its own token economy. By converting mined XMR into USDT to buy and burn QUBIC tokens, Qubic aims to create a deflationary model. Since May 18, Qubic’s share of Monero’s global hashrate surged from under 2% to over 27%, briefly making it the top Monero mining pool before dropping to seventh after community backlash, according to data from miningpoolstats.

Ivancheglo, who previously co-founded Iota, has now begun openly discussing plans to dominate 51% of Monero’s hashrate between Aug. 2 and Aug. 31, 2025, as a demonstration of Qubic’s uPoW capabilities. In posts on X, he described the move as an “economic demo” to showcase Qubic’s technology, denying malicious intent but warning that it could disrupt Monero’s network by rejecting blocks mined by other pools, potentially causing orphaned blocks and delayed transactions.

As part of this attack, Ivancheglo has said Qubic will stop reporting its Monero mining pool hashrate after Aug. 2, allegedly "to spread awareness" of the risks of a potential 51% takeover. "I, like the Monero community, am trying to find a countermeasure to Qubic's 51% domination," Ivancheglo wrote in a Monday post. "This is very important to the cryptocurrency industry because one day we all may face a non-benevolent attack."

Attack vector

Qubic’s push to control Monero’s mining hashrate has raised alarms within the Monero community, sparking concerns around risks to the network’s decentralization and security. A 51% attack refers to a situation where a single entity or colluding group controls a majority of a blockchain’s block production power, which is over half of the total mining hashrate in a proof-of-work network or a supermajority of the stake/validators in a proof-of-stake system, and uses that control to manipulate the ledger.

Some Monero community members have alleged Qubic may be renting hashrate or using bots, though no definitive evidence has surfaced to support these claims. Dan Dadybayo, a researcher and strategist at Unstoppable Wallet, noted that it wouldn't matter either way, given that Ivancheglo has created a game of incentives where Monero miners may "voluntarily surrender the network" if they see a better deal connecting to Qubic rather than Monero.

"Qubic says: 'We don’t want to harm anyone.' But intent doesn’t matter," Dadybayo wrote. "This is no longer about exploits. It’s about capital." Dadybayo estimated that with Monero's security budget sitting around $130,000 per day, "for just $7K–$10K/day, [a malicious actor could] buy majority control."

"This isn’t just a Monero story. It’s a warning to all PoW networks. Strong math isn’t enough. We need resilient, incentive-aligned infrastructure. Otherwise the next 'attack' won’t look like one at all. Just a better deal," Dadybayo argued.

XMR, Monero’s native token, traded flat and changed hands for $321 amid the debacle, according to The Block’s price page.