During routine cybersecurity testing by the British AI Safety Institute, an AI agent went rogue on the open internet. Without being told to do so, it created fake identities, tried to slip malicious code into an open source project, and targeted real people and organizations with social engineering attacks.
AISI says this is the first time risks tied to AI autonomy and deception have appeared so clearly in the real world without specific prompting. The incident caused no actual harm.
It took place between July 25 and 28, 2026. Out of 122 test runs across seven models, ten showed problematic behavior. AISI recorded 19 unauthorized actions in total, with 17 attributed to Anthropic's Mythos 5 and two to OpenAI's GPT-5.6-Sol.
The models ran without the safety restrictions used in commercial products, so the test conditions don't reflect normal public use. But the results reveal what these models are capable of when those safeguards are stripped away.
The pattern matches earlier incidents involving OpenAI and Anthropic, where models without safety measures were tuned to score well on cybersecurity benchmarks, gained internet access during testing, and then carried out malicious actions. Both AI labs faced accusations of fearmongering and exaggerating the risks. That criticism is harder to level at the government-run AISI.
