Spending 75 million to attack the network only to profit 100,000? A review of the 51% attack and defense battle between Monero and Qubic.

If the drama in the crypto world is never short of stories, then this time, the protagonist has changed to Monero.

This was not a sudden attack, but a prepared power struggle that was announced a month in advance— the attackers even declared in advance that "they would challenge the Monero network from August 2 to August 31." Their target was a rare achievement in the crypto world: to control 51% of the hash power of a privacy coin network with a market value of over 5 billion dollars.

And today, the attackers claim to have achieved this goal.

This is a long-planned attack.

We all know that in the blockchain network, all transactions must be verified by miners, a process known as "mining." The computing power of miners is referred to as hash rate; the higher the hash rate, the greater the chance of mining new blocks and earning rewards.

Monero coin is the same.

However, compared to other coins, Monero has a design to prevent large mining pools from acting maliciously - it does not support dedicated mining machines (ASICs) and can only be mined using ordinary computer CPUs or GPUs. The original intention of this rule is to prevent miners from gathering in a single large mining pool, which means that theoretically anyone can participate in mining with their own computer, making the network fairer and more decentralized.

However, this mechanism also has an idealized attack method, which is to rent or mobilize a large number of ordinary servers (such as cloud computing resources, idle PCs, miner computers) in a short period of time. And this is precisely the method used by the attackers in this case.

Now let's look at this long-planned attacker, called Qubic.

The initiator of this action is Qubic, an independent blockchain project not originally created to attack Monero. It is led by Sergey Ivancheglo, co-founder of IOTA and a veteran crypto developer (nicknamed Come-From-Beyond), and utilizes the "Useful Proof of Work" (UPoW) mechanism, allowing miners' computational power to be used not only to solve mathematical problems but also to train its artificial intelligence system "Aigarth", achieving two goals at once.

So why does it have a connection with Monero and launch a "war" on its hashrate?

In fact, this is an "economic demonstration" of Qubic showcasing its UPoW model capabilities. Starting from May 2025, it successfully attracted a large number of miners to join by using its network computing power for CPU mining of 门罗币, earning both 门罗币 and $QUBIC token rewards just from mining. The 门罗币 mined by the miners will be sold for stablecoins, which will then be used to repurchase and destroy Qubic coins, creating a self-reinforcing economic cycle.

After Qubic announced its "challenge" to the Monero network from August 2 to August 31, some members of the Monero community began to monitor the situation on the chain around the clock. Someone stated on Reddit that they would keep an eye on every block, especially paying attention to the occurrence of orphan blocks. Initially, everything was normal, but one early morning, they noticed a chain reorganization. In theory, chain reorganizations are not uncommon in the Monero network, for example, when two miners mine blocks at the same time, the system will choose one and discard the other. However, the timing of this event is suspicious, seemingly related to Qubic's testing of the ability to insert alternative blocks and fork the blockchain. Although the alternative block was ultimately rejected, it indicates that Qubic is attempting to take action.

Monero coin's block status

The monitor also found that Monero was supposed to produce a block every two minutes, but the block generation speed has noticeably increased recently, and the network seems to have detected signs of potential attack pressure. This made him confident that Qubic was indeed engaging in some form of interference. Another participant pointed out that the only orphan block that occurred was 12 hours before Qubic publicly claimed it would launch an attack.

In terms of computing power data, the community has also observed that Qubic stopped reporting its computing power to public mining pool statistic websites at the beginning of August, which has prevented outsiders from directly seeing their true mining capabilities. Some speculate that this may be to hide peak computing power and create a sense of opacity, while showcasing more favorable numbers through a self-controlled website. Members of the Monero core team analyzed that their computing power is not constant, but rather switches regularly between peaks and valleys. This "switch" mode is more threatening than stable mining.

The result of this premeditated attack by Qubic to "show off" was that during the period from May to July, Qubic accounted for nearly 40% of the Monero network's hash power. By August, Qubic claimed to have reached 52.72%, directly crossing the 51% "control threshold"—which means it could technically reorganize the chain, conduct double-spending attacks, or censor transactions. Qubic stated that this was to simulate the attacks that the Monero network might face and to identify security weaknesses early.

Is Qubic really just bluffing?

So did Qubic really succeed in a 51% attack? Many people still hold a skeptical attitude towards this, believing that it was just a deliberately deceptive marketing ploy.

@VictorMoneroXMR raised a question with the screenshot below. When the total hash rate of other Monero mining pools is shown as 4.41 GH/s and the total network hash rate is 5.35 GH/s, Qubic's data dashboard shows that it has a hash rate of 2.45 GH/s under the same total network hash rate. This data clearly does not match, and it is possible that Qubic's data dashboard did not include its own hash rate in the total network hash rate. If we make corrections based on this assumption, Qubic's hash rate actually only accounts for about 30% of the total hash rate.

Aside from the data cloud, the most direct on-chain evidence currently is that Monero has experienced a consecutive block reorganization of 6 blocks, but this still cannot 100% confirm that Qubit has the capability to launch a 51% attack.

This point is also supported by the real-time monitoring post of blocks in the Monero Reddit community.

Throughout the Qubic challenge, the community did not see a sustained, significant increase in orphan blocks or chain reorganization, with only one suspected reorg, and the alternative block was rejected. Core developers and the community observed that Qubic was close to or even slightly above 50% of the hash rate at certain times (Qubic claims to have reached 52.72%), and even if it briefly exceeded 51%, if only for a few minutes or a few blocks, it may not be able to execute an effective attack.

In other words, there is currently no evidence to show that they maintain stability above 51% for a long enough time to launch a successful attack.

The current consensus in the Monero coin community is that Qubic may exceed 51% in a short period, but no effective attack has been executed; it is more like a demonstration of computing power and psychological warfare. The attacking party may showcase exaggerated percentage screenshots on their own website to create the impression that they have taken control of the network.

Flower 75 million to lose 100,000 in a losing deal?

The attack cost of Qubic has also sparked a lot of discussion on social media platforms.

The analysis from the Roin community generally believes that the cost to maintain the current computing power controlled by Qubic is extremely high. Based on the current network difficulty, the daily block reward value of Monero is approximately $150,000. If an attacker wants to continuously maintain over 50% of the total network computing power, it means they need to produce blocks equivalent to half or more of the total network every day, and the costs for hardware, electricity, and operation are astonishingly high.

According to calculations by Yu Xian, the founder of the security company SlowMist, the cost of an attack of this scale could reach up to 75 million USD per day, which is a figure that is almost impossible to recover solely through speculative mining.

Due to the exorbitant nature of this number, let's analyze it from other angles. First, let's look at Crypto51, a website specifically designed to estimate the cost of conducting 51% attacks on different PoW coins. For some mainstream or mid-to-small market cap coins, it provides a reference for the cost of renting computing power per hour. For example: Ethereum Classic (market cap of approximately hundreds of millions of dollars): about $11,563 per hour; Litecoin: about $131,413 per hour.

Although Crypto51 does not have specific data on Monero, it can be seen that even a medium-sized PoW network generally has an attack cost that is usually far below the level of tens of millions of dollars per day.

Based on discussions on Reddit, a community friend attempted to estimate the attack cost of CPU PoW (like Monero) in the following way: assuming the use of an AMD Threadripper 3990X (with a performance of about 64 KH/s), to achieve 51% of the network would require about 44,302 such CPU machines. The equipment acquisition cost alone is approximately $220 million (44,302 × $5,000). If other hardware costs, venue rentals, and electricity expenses are included, an additional tens of millions of dollars would be needed. The electricity cost is expected to be around $100,000 per day.

So, with an attack cost of 75 million dollars a day, how much can Qubic profit from it?

According to the current tail emission rules of Monero, the block time is approximately 2 minutes, and the reward for each block is fixed at 0.6 XMR. If Qubic controls more than 51% of the hash power, it means they have the ability to mine all Monero blocks in a day, which is approximately 432 XMR.

At the time we wrote this article, the price of Monero was around 246 USD. Based on the current price of Monero, if Qubit monopolized all of the Monero output within a day, it could only profit around 106,000 USD.

According to Qubic's official "Epoch 172 Report", Qubic distributes the Monero coins it mined in a 50% - 50% ratio, with half used for the buyback and destruction of $QUBIC, and the other half for miner incentives. However, the miners' rewards are still paid in $QUBIC.

In other words, with a market value of less than $300 million, $QUBIC has the capability to produce Monero, which has a monopoly market value of nearly $4.6 billion. Theoretically, they could go all out and destroy $53,000 worth of $QUBIC in a day, and $1.509 million worth of $QUBIC in a month, which is truly insane.

The counterattack of Monero, an ongoing battle.

Therefore, the outside world generally believes that Qubic's motivation is not just to directly mine Monero for profit, but to support a combination economic model of "computing power + tokens": Qubic does not directly pay miners with fiat currency, but uses its own token $QUBIC as a reward, and artificially maintains the secondary market price of the token—once the price stabilizes or even rises, it can exchange for substantial real computing power support at a relatively low token issuance cost. The core of this approach is that the rewards obtained by miners in the Qubic mining pool for mining Monero will be exchanged for Qubic tokens, and if the token price remains high, the nominal returns for miners will be considerable, naturally attracting them.

In terms of profit models, Qubic does not necessarily rely on Monero's block rewards to make money, but instead leverages this event to create buzz around its tokens, increase trading volume and price, and thereby attract more speculative buying.

As long as the market value and liquidity of Qubic coin are maintained at a level sufficient to pay the miners, this large-scale computing power occupation can continue. However, this model is built on a highly fragile foundation of confidence: if miners feel that the price of Qubic coin is difficult to maintain, they will collectively sell off to exchange for more stable assets, which will trigger a price crash and lead to a "first come, first served" stampede.

This is a blatant and domineering "siphoning" of computing power, which has naturally aroused strong dissatisfaction and counterattacks from the Monero community.

Interestingly, during the Qubic attack on Monero coin, it also suffered anonymous attacks.

According to Qubic founder Sergey Ivancheglo (nicknamed Come-From-Beyond), their mining pool has experienced a DDoS attack (Distributed Denial of Service attack) at this stage. The data provided by Qubic indicates that the hash rate of their mining pool has dropped from approximately 2.6 GH/s to 0.8 GH/s, a decrease of over 70%. Therefore, he believes that someone intentionally used a cyber attack to disrupt their hash rate operations.

The attacker Qubic founder Sergey Ivancheglo stated that he was also attacked.

During the accusations, Ivancheglo even specifically doubted that the main developer of the Monero mining software XMRig, Sergei Chernykh (nickname sech1), was the mastermind behind it. However, sech1 responded immediately, clearly denying any involvement in illegal attacks: "I am not the only one in the Monero community who is dissatisfied with Qubic's actions. But I would never resort to illegal means such as DDoS attacks. Others might."

The main developer of the Monero mining software XMRig stated, "I am not the only one in the Monero community who is dissatisfied with Qubic's approach."

At the same time, it seems that the Monero community is also discussing that all Monero users should come together and completely eliminate Qubic:

"We need a movement #ShortQubic, they want to provoke us, we can only fight back. After all, the Monero community is larger." "Where to short Qubic? Why don't we collectively short Qubic Coin, even with leverage? That would completely kill miners' enthusiasm."

Monero coin community discusses how to fight back

Interestingly, a member of the Monero community pointed out that there may also be ideological reasons behind the Qubic attack on Monero.

The Qubic official website shows that the team has many members, but most use pseudonyms, with only two using their real names. One is the Qubic founder Sergey Ivancheglo mentioned earlier, and the other is Qubic scientist David Vivancos, who has been advocating for the integration of humans and machines. David Vivancos is described as a "technocrat," believing in a model of social management driven by technical experts and data. This ideology has been criticized for being contrary to the decentralization, privacy, and community autonomy pursued by Monero, and even carries a dystopian flavor.

The offensive and defensive battle is not over; the smoke of psychological warfare still lingers. Next, will the Monero community counter Qubic through technology, finance, or public opinion? And how long can Qubic's "power siphon" be maintained? Rhythm BlockBeats will continue to pay attention.