Bitcoin is trusted by governments and financial institutions. Prominent investors call it “digital gold,” and some even claim it’s better than gold. Despite all this, Bitcoin still faces various security threats. A lot has been said recently about the potential threat of quantum computers. However, Professor Campbell Harvey of Duke University revealed another concern: 51% attacks against the Bitcoin network are relatively cheap.
summary
- If successful, a 51% attack would allow an attacker to take control of the Bitcoin blockchain (or another proof-of-work based blockchain). To be successful, an attacker must control over 50% of the mining hash rate, which comes at a cost.
- In the past, Bitcoin Gold and Ethereum Classic experienced successful 51% attacks resulting in coin theft due to double spending. Throughout history, the Bitcoin blockchain has remained secure from 51% attacks.
- According to Harvey, to monopolize hashrate generation for a week, an attacker would need to spend “only” $6 billion, less than 0.5% of Bitcoin’s market capitalization. Harvey provided the possibility of practical use of such an attack.
Campbell Harvey, a professor at Duke University’s Fuqua School of Business, published a paper focused on potential threats to Bitcoin. In his summary, Harvey likens Bitcoin to gold, but outlines that Bitcoin faces its own unique threats: quantum computers and, more importantly, the possibility of a 51% attack. He also recognizes that Bitcoin has advantages over gold. For example, he says that while “modern alchemy” allows for the production of more gold, the supply of Bitcoin cannot exceed 21 million units.
read more: Quantum Countdown: How Bitcoin’s 15-year shield stands up to its biggest threat yet
What is a 51% attack?
Mining Bitcoin is expensive and requires special hardware, so miners don’t have the opportunity to tinker with ledger data. Each node “votes” via its computing power (hashrate) to validate transactions for new blocks, and the majority of miners vote for correct data. Miners rely on the integrity of the Bitcoin blockchain, so they have an incentive to vote for correct data, which brings value.
However, once half of the total hashrate in the system is controlled by a single entity (either an individual or a group of plotters), it has the power to change the records on the Bitcoin ledger. This allows malicious parties to move someone else’s Bitcoin and essentially steal their Bitcoin.
Although some have criticized Bitcoin for its low level of decentralization, in the 16 years that Bitcoin has existed, no one has succeeded in controlling the Bitcoin blockchain.
In the early days of Bitcoin, mining was accessible to any PC owner. However, because mining is based on competition and requires the luckiest miner to have a higher hashrate level than most of their rivals, computers, and even GPUs and FPGAs, quickly became obsolete for mining. In 2013, the first ASICs (devices specialized for Bitcoin mining) appeared on the market. Bitcoin mining soon turned into a multi-million dollar industry, requiring significant investment and equipment filled with whirring ASIC devices. In October 2025, Bitcoin mining difficulty reached a new high.
Bitcoin mining difficulty has been adjusted:
150T at +5.97% (new ATH).
It’s good to see prices rising to offset the pressure on hashprice. pic.twitter.com/3qrdKirgnR
— Javier Hermosa (@JavierHermosa21) October 2, 2025
This makes hacking Bitcoin with a 51% attack a difficult and expensive task. As the difficulty of mining increases, the cost of a 51% attack also increases every year.
Campbell Harvey’s Discovery
51% attacks are costly, but the cost is not unimaginable. Networks like Bitcoin Gold and Ethereum Classic have suffered several 51% attacks since 2017. In each individual case, more than 1 million cryptocurrencies were stolen. In August 2025, the Qubic mining pool claimed to have captured over 50% of the hashing power of the Monero network.
read more: Monero in trouble: Kraken freezes deposits, Qubic gains 51% hashrate
Professor Harvey calculated the costs and concluded that it would cost “only” $6 billion to dominate the Bitcoin blockchain for one week.
“Hardware is the biggest expense, about $4.6 billion at current prices. It would cost $1.34 billion to build the data center, and about $130 million per week in electricity to run the hardware and maintain the data center. In total, a weekly attack would cost about $6 billion, or 0.26% of the total value of the Bitcoin network.”
This study is based on the following indicators:
- Annual production of Bitcoin is 164,363BTC
- Energy consumption is 166.4TWh
- Total cost: $12 trillion
- Total energy cost is $8.4 trillion
- Total cost per unit is $73,000 per BTC unit
Harvey pointed out that if the 51% attack on Bitcoin was successful, the price would drop significantly and hackers could still profit from it and recover more than $6 billion. Harvey estimated the daily volume of BTC perpetual futures at $60 billion and the daily volume of traditional BTC futures at $10 billion. Harvey believes short positions in these markets before a 51% attack could not only return the $6 billion, but also generate significant profits for the attackers. Harvey added that the motive may not be profit-related.
But critics of Mr Harvey’s warnings argued that setting up such a large-scale mining operation would take years and would not be ignored. More than that, it may be difficult to short sell such a large amount of BTC while the 51% attack continues. This is because there is a high possibility that the exchange will flag the operation as market manipulation and disallow it.
Commenting on Harvey’s research, Matt Prusak, president of American Bitcoin, told Bloomberg, “My view is that economic feasibility undermines the 51% theory. I live in the real world and I’m not worried.”
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