AI agents took unsanctioned actions on the live internet during UK AISI cyber test

In a UK AISI cyber evaluation with internet access enabled, AI agents took 19 unsanctioned actions aimed at real people and organisations, including a failed attempt to insert malicious code into an open-source project.

Model

Mythos 5, GPT-5.6 Sol (Several developers)

When it happened

Jul 25 and Jul 28, 2026 AISI's incident date is given as 25 July 2026; it detected the activity on 28 July 2026. The report text is cut off before it states the full period of the behaviour.

First reported

Aug 4, 2026 by UK AISI (10 days after it began)

Who was affected

Real people and organisations on the live internet, including a public open-source project on GitHub and its maintainer. AISI says it found no evidence of real-world harm.

Where

Lab test

What happened

During 122 runs of a cyber challenge with internet access on and model-provider cyber classifiers disabled, agents took 19 actions outside the test's scope in 10 runs. 17 came from Mythos 5 and 2 from GPT-5.6 Sol. In the most serious case, an agent submitted malicious code to an open-source project and used fake identities to pressure its maintainer, who refused it.