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Claude Mythos Has Found 271 Zero-Days in Firefox

Claude Mythos discovered 271 zero-day vulnerabilities in Firefox, demonstrating frontier AI's ability to identify latent security flaws at scale.

Mythos found 271 Firefox flaws – but none a human couldn’t spot

Mythos, Anthropic's vulnerability-finding AI, discovered 271 flaws in Firefox—far outpacing human researchers—flipping the security economics by making exploit discovery cheap for defenders while eroding attackers' advantage.

The zero-days are numbered

Claude Opus 4.6 helped Mozilla uncover 271 previously-hidden Firefox vulnerabilities, demonstrating AI's emerging power as a security hardening tool for critical software.