Understanding the Monero 51% Attack

Privacy-focused cryptocurrency Monero has suffered a 51% attack after Qubic, an AI-powered blockchain, gained control of more than half of its mining power. 

Qubic confirmed the situation on X and in a blog post. This control means Qubic could temporarily rewrite parts of Monero’s blockchain history. On August 11, Qubic reorganized the chain by six blocks and removed about 60 blocks from the record. Such control makes it possible to censor transactions or attempt double-spending. However, Qubic did not create any fake transactions on Monero.

Interestingly, the attack on Monero took weeks of preparation. During this time, Qubic also faced a strong distributed denial-of-service (DDoS) attack on its systems. They stayed online through it all.

What is Qubic?

Qubic is a blockchain that uses a mining model called Useful Proof of Work (UPoW). Instead of only solving random puzzles, miners also do useful tasks, like running AI computations. Qubic’s goal is to host a decentralized AI called AIGarth.

The Monero attack began as an experiment to test their system in the real world. Qubic split its computing power between mining Monero and training AIGarth. At times, this strategy made mining through Qubic nearly three times more profitable than normal Monero mining. This approach pulled many miners into their pool.

How the Attack Worked

With a majority of the hashrate, Qubic used a strategy called Selfish Mining. This means secretly mining blocks and releasing them at the right time to outpace others. This caused other miners’ blocks to become “orphaned,” meaning they were discarded from the main chain.

The attack was expensive, about $75 million per day. But it was also profitable through block rewards. At one point, Qubic mined more than 51% of blocks in a 122-block window.

Aftermath and Impact

Qubic chose not to take full control of Monero’s consensus. They said doing so might hurt Monero’s value. Instead, they suggested a new model where their miners could help secure Monero while earning rewards through Qubic pools.

The Monero network’s core privacy and speed stayed intact. But the attack raised urgent questions about security, even for large blockchains.

This case showed three key lessons: useful computations can work in mining, economic incentives decide who controls a network, and strong infrastructure can survive major cyberattacks.

It is now a landmark moment in blockchain history: a smaller AI protocol proving it could outcompete a much bigger privacy coin. Beyond that, it serves as a warning that no network is completely safe from economically driven majority attacks.

As expected, Monero’s $XMR reacted badly to the news, falling by 12% shortly after the news. The situation comes as Monero faces bans on being listed on centralized exchanges due to its privacy nature. Exchanges like OKX do not list $XMR due to concerns that it could be used for laundering and crime.

All of these put Monero’s stability at risk. For Qubic, the control is a big win. A project with less than a $300 million market cap now takes control of a project worth $6 billion.

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