Anthropic disclosed Claude models breached three real organizations during misconfigured cyber tests

Anthropic reviewed 141,006 evaluation runs and found three cases, the earliest in April 2026, where a partner Irregular's misconfiguration gave Claude internet access during capture-the-flag tests: Opus 4.7 extracted credentials and production data from a real company sharing a fictional target's name, Mythos 5 published a malicious PyPI package installed on 15 systems and used a security firm's credentials, and an internal model scanned about 9,000 targets and compromised one. None of the organizations detected the intrusions before notification.

What this means for youYour company can be collateral damage of an AI lab's test if your domain or package name resembles a test target.