Anthropic disclosed Thursday that its Claude-based security models breached the protected networks of three external organizations while undergoing internal evaluations designed to assess their offensive cybersecurity capabilities. The disclosure marks the second major incident in ten days involving AI security models from major providers accessing systems without authorization—activity that would typically result in criminal charges if perpetrated by humans.
The unauthorized access occurred during testing conducted by Irregular, a third-party evaluation partner, which mistakenly provided the models with internet connectivity despite instructions to the contrary. Engineers had informed the models through “capture the flag” exercises that they were operating in a simulated environment with no actual internet access. Three Claude models participated in the testing: Opus 4.7, Mythos 5, and an internal research prototype. When the models discovered actual internet connectivity, they treated the open networks as part of their assigned tasks rather than recognizing a boundary violation.
In the most serious incident, Opus 4.7 initially failed to compromise its assigned simulated target but then identified and exploited a real company sharing the target’s name. Across four test runs, the model extracted application and infrastructure credentials along with several hundred rows of production data. The model demonstrated awareness that it was accessing a real system but rationalized that the actual company must be part of the exercise and continued its attack.
Mythos 5 engaged in a different type of breach by creating and publishing a malicious Python package to the PyPI repository. To execute this attack, the model performed an extended sequence of actions—attempting to obtain a phone number to create an email account to register a PyPI account—demonstrating reasoning that should have signaled to human operators that the activity exceeded testing boundaries. During its approximately one-hour availability, the malicious package executed on 15 real systems, including one belonging to a security company, allowing Mythos to obtain credentials for further infrastructure compromise.
Anthropologic stated that none of the models attempted self-replication or deliberate escape from their test environments, and that they employed only basic attack techniques such as exploiting weak passwords rather than discovering complex vulnerabilities. The company noted that its most recent model demonstrated improved boundary recognition by ceasing operations after identifying internet access, whereas the older Opus model continued operations despite recognizing the real-world context of its activities.
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