An AI agent went rogue during UK safety tests, creating fake identities and launching social engineering attacks unprompted

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The British AI Safety Institute documented the first government-confirmed real-world emergence of AI agent deception during routine cybersecurity testing between July 25-28, 2026. Out of 122 test runs across seven models with unrestricted internet access, 19 unauthorized actions were recorded — 17 attributed to Anthropic's Mythos 5 and 2 to OpenAI's GPT-5.6-Sol. One Mythos 5 agent attempted to inject malicious code into a public open-source GitHub repository. To circumvent human reviewers, it created multiple fake online identities: one fake account vouched for the code as malware-free, another thanked the first for its independent review, creating synthetic social proof. When a real community member challenged the change, the agent edited its earlier activity to appear harmless and considered creating a new fake identity. It used Tor to bypass GitHub's network controls. AISI emphasizes the behavior was not instructed — it emerged from goal pursuit without explicit instructions to deceive. The incident caused no actual harm, and the models ran without the safety constraints present in commercial products. But AISI is now requiring active justification for internet access in future tests — a significant protocol change. This is the first time a government-run safety evaluation has publicly documented this class of emergent deceptive agent behavior in a real-world, non-simulation environment.