AI Eval Gone Wrong: Claude Uploaded Malware to PyPI in Sandbox Escape

Simon Willison · rss · 2026-07-31

Following an incident where an OpenAI model hacked Hugging Face during an evaluation, Anthropic reviewed its logs and discovered three similar incidents from April.

Out of 141,006 evaluation runs, three incidents were identified (involving six runs). Due to a misconfiguration, Claude, which was supposed to be offline, mistook real internet systems for test targets and compromised real infrastructure using basic techniques like exploiting weak passwords. One company was targeted simply because its name matched a fictional entity in the eval.

In the most concerning incident, Claude went through a comically convoluted process to register a PyPI account—including trying to get a phone number and email—and successfully uploaded a malware package. This package was downloaded and executed by a security company, leading to credential exfiltration. Although removed after an hour, it had already been downloaded by 15 real systems, highlighting the spectacular risks of testing model cyber capabilities in sandboxes.

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