April 21, 2026 Google has warned that advances in quantum computing could expose Bitcoin to theft during active transactions, urging the cryptocurrency community to begin upgrading its security model. The company’s white paper states that while large-scale quantum attacks are not yet happening, the time required to migrate systems may exceed the time left before the threat becomes practical.
The warning centres on how quantum computers could break the cryptographic protections that secure Bitcoin transactions. University of Auckland mathematician Steven Galbraith said the risk is credible but not immediate, noting there is currently no evidence of a quantum system capable of executing such attacks. However, he added that attackers may already be collecting encrypted data now with the intention of decrypting it later when the technology matures.
The concern is particularly acute for Bitcoin because of how its network operates. Unlike banks or large technology platforms that can roll out centralised security upgrades, Bitcoin is maintained by a decentralised network of participants, making coordinated changes slower and more complex. While post-quantum cryptography (PQC) is available and already protects about 20 per cent of internet traffic, applying it across a global blockchain system could take years.
The paper highlights two primary risk scenarios. First, active transactions typically taking around 10 minutes to confirm could be intercepted and compromised by a sufficiently advanced quantum system. Second, dormant Bitcoin holdings present a larger long-term target. Approximately 1.7 million Bitcoin have not moved since 2009, forming what the report describes as a fixed, multi-billion-dollar pool vulnerable to future “at-rest” quantum attacks.
Some of those assets are believed to include roughly one million Bitcoin linked to Satoshi Nakamoto. According to Cryptocurrency NZ co-founder Nicolas Turnbull, any successful breach of such holdings could significantly disrupt the market. He noted that a sudden release of that volume could drive prices down sharply, even as opportunistic buyers move in.
Efforts to mitigate the risk are underway at the wallet level, where users can adopt newer standards designed to scale toward quantum resistance. However, these measures do not address dormant coins or older transactions that cannot be easily migrated. The absence of central governance within the Bitcoin ecosystem further complicates any large-scale transition.
Google’s report argues that the migration window remains open but is shrinking. It recommends that cryptocurrency communities begin transitioning to post-quantum cryptographic systems immediately, while timely implementation is still achievable.
