Reused bitcoin addresses are quietly increasing quantum risk

Despite billions spent on blockchain improvements and security measures, crypto criminals still steal billions of dollars from the crypto ecosystem each year, and that didn`t change in 2025. In fact, with over $4 billion in total losses from hacks, fraud, scams, money laundering, and ransomware, 2025 was the worst year for crypto illicit activity ever recorded.

However, cryptocurrencies, and Bitcoin in particular, could face a completely new kind of threat in the future - quantum computers. While it's not an urgent danger like the billions stolen in everyday crypto scams, it's still serious enough that major institutions are talking about it. And the reason is simple: the damage quantum machines could potentially cause to Bitcoin`s security model is just mind-blowing.

According to data presented by TechGaged, roughly 4.9 million BTC worth over $455 billion is currently exposed to a potential quantum attack due to address reuse alone, 16% more than just five years ago.

Reused Addresses Add Roughly 100,000 BTC to Quantum Exposure Each Year
Ever since Google announced “quantum supremacy” in late 2019, quantum computers have become a hot topic in the tech space. However, Shor’s algorithm, one of the most famous quantum methods these machines use, has also placed them on the list of major potential security threats.

The algorithm itself is the main reason people worry about quantum computers. It could break the math that protects most online security, including Bitcoin, shockingly fast. On normal computers, cracking this kind of security would take an unreal amount of time.

So, what does that mean in Bitcoin`s case? A powerful enough quantum computer running Shor's algorithm could potentially derive private keys from exposed public keys, making some older, reused addresses much easier targets. While such a machine is still not publicly available, experts and major institutions, including BlackRock, have already raised the big question: If someone had a powerful quantum computer right now, how much Bitcoin could they steal? And the answer is mind-blowing.

According to the findings, the amount of Bitcoin potentially vulnerable to a quantum attack has grown significantly over time, rising from roughly 3.5 million BTC in 2021 to around 6.8 million BTC in 2026. Around 2 million BTC is exposed due to older address types, and that number hasn`t changed much over the years. These coins were probably mined early and never moved, still sitting in the original old addresses.

But the most worrying part is that Bitcoin's quantum exposure keeps growing, mostly due to user behavior, especially the reuse of addresses. Reused Bitcoin addresses are more exposed because their public key becomes visible on the blockchain. In a quantum attack scenario, a machine using Shor`s algorithm could potentially use that public key to calculate the private key, sign a transaction and steal the coins from that address. And while many would assume people have learned not to reuse addresses, the data shows just the opposite.

Between 2011 and 2016 alone, the amount of BTC sitting in reused addresses jumped by roughly 2.9 million, rising from 800,000 to 3.7 million BTC. Although the trend slowed down between 2016 and 2020, adding roughly 500,000 BTC to the risk, it picked up again from there.

Between 2020 and 2026, the number of BTC exposed in reused addresses jumped by another 700,000, reaching 4.9 million this year. That`s roughly 100,000 BTC added to quantum exposure each year, worth roughly $9.1 billion at the current BTC price. This proves that while Bitcoin has evolved, user habits like address reuse are still quietly building into a long-term risk.

“Quantum computing is not an immediate threat to Bitcoin, but the exposure we’re tracking is structural and cumulative,” said Jastra Kranjec, Senior Research Analyst at Techgaged.com. “The real risk is not that a quantum attack happens tomorrow, but that millions of bitcoins remain parked in reused or legacy addresses year after year. If quantum-capable systems emerge before users migrate to safer practices or the network adopts quantum-resistant signatures, the potential impact could be unprecedented.”

Old and Reused Addresses Put One-Third of Bitcoin`s Total Value at Quantum Risk
While sceptics argue that a quantum computer strong enough to pull off such an attack is still not publicly available, meaning experts are still discussing a scenario that lies somewhere in the future, if Bitcoin user behavior doesn't change, these numbers will continue to build into a mind-blowing risk.

Measured in US dollars, at the current BTC price of $91,000, more than $618 billion worth of Bitcoin, or one-third of its total market cap, is potentially exposed to a quantum attack due to old or reused addresses. This figure alone is enough to make many believe that Bitcoin will eventually need an upgrade to quantum-resistant signatures, even if a real-world attack doesn`t happen anytime soon.