As the timeline for Q-Day draws closer, many security executives are focusing on only one aspect of the quantum computing threat: data decryption. While that threat is real, and “harvest now, decrypt later” attacks are already underway, the arrival of cryptographically-relevant quantum computers (CRQCs) introduces a far broader set of risks than the decryption of stored data alone. It gives nation-state and criminal actors the ability to break the security mechanisms that all modern digital systems depend on today.

Quantum computing threatens the cryptographic foundation that digital systems rely on to verify identity, authenticate users and systems, validate information, and establish trust. In practical terms, it undermines the mechanisms that ensure network users are legitimate, websites are authentic, communications reach the correct destination, and critical data has not been altered.

AI further amplifies these risks by identifying targets, prioritizing opportunities, and orchestrating attacks at machine speed and scale. Together, quantum computing and AI will create an entirely new class of cyber attacks that most enterprises are not yet prepared to defend against.

Here are five critical threats security leaders should expect.

Identity Forgery at Scale

Employee account compromise is already one of the most significant threats facing enterprises today. In a post-quantum world, it becomes dramatically more dangerous unless organizations have fully migrated to post-quantum cryptography.

Today, threat actors typically rely on social engineering and credential theft to pull off these attacks. After Q-Day, they can use quantum algorithms to derive private keys from the public keys contained in certificates and generate cryptographically-valid identities at will that appear completely legitimate to enterprise systems.

The result is the ultimate insider attack, powered by an essentially unlimited forgery capability. Enterprise systems and security tools will be unable to distinguish a legitimate user from an attacker. AI can automate and scale these attacks across entire industries.

Trusted Systems Become Attack Vectors

The implications of these identity attacks extend far beyond employee accounts. Software update mechanisms, API integrations, cloud-to-cloud communications, machine identities, device certificates, industrial control systems, and third-party vendor connections all depend on cryptographic trust.

A forged certificate tied to a high-value trust relationship identified by AI could allow attackers to impersonate software, applications, devices, or business partners and gain deep access into enterprise environments. Because the attacker will operate as a legitimate entity on the network, traditional indicators of compromise may never appear, allowing criminals to move laterally across systems and access sensitive resources without detection. AI can rapidly identify and prioritize the most valuable trust relationships to exploit.

Achieving a breach at this scale today typically requires exploiting a critical vulnerability or compromising a key vendor. Quantum-enabled forgery changes that equation by attacking the trust layer itself.

When Data Can No Longer Be Trusted

The disruption caused by ransomware may pale in comparison to the long-term consequences of data integrity attacks.

Quantum-enabled data manipulation can leave systems appearing to operate normally while quietly corrupting critical processes and influencing key decisions. In real terms, this means attackers can alter financial transactions during processing, inject false data into supply chains, manipulate industrial systems while sensors report normal activity, and feed medical systems fraudulent treatment information that places patients at risk.

AI further amplifies these attacks, enabling them to be executed with greater scale and precision while remaining difficult to detect. The consequences range from operational disruption and financial loss to regulatory exposure and even threats to human safety.

Blinding Security Teams

Cybersecurity systems themselves are no less vulnerable.

In a post-quantum environment, attackers can manipulate security logs, audit records, telemetry streams and forensic evidence to erase signs of malicious activity while maintaining access to the network.

This creates a fundamentally different challenge for defenders. AI can automate and continuously refine these attacks, helping adversaries identify targets, adapt attack paths, and obscure evidence of their activity in real-time. If those records can no longer be trusted, organizations may not know whether a compromise has occurred, who was responsible, or whether the threat has been contained.

The result is an attack that becomes far more difficult to detect, investigate and remediate.

Compromised Digital Trust

Imagine a world where employees can no longer be certain they are logging into Microsoft 365 rather than an attacker-controlled environment, or where a finance manager cannot verify that a five-figure wire transfer is actually being routed through her bank.

Quantum-enabled forgery of cryptographic certificates allows attackers to create trusted-looking connections that intercept, redirect, or modify traffic while appearing legitimate to users and security tools alike.

The threat is not simply eavesdropping. It is the manipulation of entire business processes that depend on cloud platforms, SaaS applications, APIs, financial systems and partner ecosystems. AI can accelerate these attacks across organizations by identifying high-value trust relationships and automating exploitation at scale. If enterprises can no longer reliably verify who is on the other end of a connection, every workflow that depends on external systems becomes a target.

What Security Leaders Should Do Now

Organizations have spent decades building security controls that depend on cryptographic validation. Quantum-enabled forgery challenges that foundation by attacking the trust mechanisms directly.

Security leaders should take several steps now:

1. Prioritize signing infrastructure alongside encryption: Much of the industry’s attention has focused on protecting encrypted communications, but digital signatures and certificates are equally critical.
2. Build for crypto-agility: Organizations should design systems so cryptographic algorithms can be replaced when they change or are broken without extensive re-engineering and network operations downtime.
3. Extend post-quantum requirements across the supply chain: Post-quantum readiness should become a procurement and third-party risk management requirement.
4. Implement independent integrity verification: Organizations will need additional methods for validating critical data, operational systems, financial transactions, logs and telemetry beyond cryptographic signatures alone.
5. Address the network layer explicitly: Post-quantum authentication for TLS, DNS, routing infrastructure and other trust-dependent internet services should be treated as a strategic priority.

The companies best prepared for the post-quantum era will not be the ones that focus solely on protecting data. They will be the ones that secure and rebuild the trust infrastructure on which modern business depends.