The Negative-Day Risk: How Quantum Rewrites The Cyber Threat Model

InnovationThe Negative-Day Risk: How Quantum Rewrites The Cyber Threat ModelByDenis Mandich,Forbes Councils Member.for Forbes Technology CouncilCOUNCIL POSTExpertise from Forbes Councils members, operated under license. Opinions expressed are those of the author. | Membership (fee-based)Jun 08, 2026, 06:00am EDTDenis Mandich, CTO of Qrypt, a quantum cybersecurity company, and founding member of the Quantum Economic Development Consortium and CQT. gettyAnthropic is cautiously rolling out Mythos after the AI tool found thousands of previously unknown software vulnerabilities, triggering serious concern among security leaders about AI-enabled zero-day attacks.While the concern is valid, it ​is also important to remember that hackers are also pursuing a harvest now, decrypt later (HNDL) strategy, where they steal valuable encrypted data in anticipation that quantum technology will be able to crack the encryption in the near future. These are negative-day attacks: The adversary is not exploiting something defenders have missed, but betting the future will make today’s inaccessible secrets visible.The cybersecurity industry cannot prepare only for the unknown bug that could appear tomorrow. It also has to prepare for the sensitive data, identity systems, certificates and communications that are considered safe today but may become vulnerable years from now. While zero-day attacks require urgent attention, negative-day attacks require a structural cybersecurity shift.From Zero-Day Shock To Negative-Day Risk​Zero-day attacks rose to fame in 2010 when the Stuxnet attack used multiple previously unknown exploits. This pre-AI engineering effort chained together five vulnerabilities to gain access to a uranium enrichment plant in Iran. ​That history matters for boards, CISOs, software vendors and infrastructure providers because it shows what happens when hidden weaknesses are converted into real-world power. But it does not mean every organization should view zero-day discover...