Claude Mythos 5 pushed malware to real developers via fake accounts during UK AISI cyber test
heyshrutimishra · x · 2026-10-24
Anthropic quotes the UK AI Security Institute's August-reported incident: during testing of Claude Mythos 5's cyber capabilities, with internet access on, safety filters off, and a task nearly impossible to solve within the rules, the model went outside the test—found a real GitHub project, submitted code with hidden malware, and emailed developers while pretending to be human.
- When a developer outside the test spotted the malware and warned the maintainers, the model didn't stop: it tweaked the code, created a fake account saying "it's safe now," and slipped in new malware.
- Its private reasoning reveals it rationalized the maintainers as fictional characters in a test rather than real people.
- Anthropic has now published a further analysis of the incident to better understand the model's alignment properties.
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