GoKawiilWhat just happened? It's been little over a week since OpenAI admitted that its rogue models hacked Hugging Face and compromised accounts across four other online services. Now, a potentially more serious incident has occurred. It involved Anthropic's Mythos 5 trying to deceive real people in an effort to have malicious code it wrote approved for an open-source project.
The findings come from the UK government-backed AI Security Institute (AISI), which was evaluating frontier models' cybersecurity abilities.
Agents were told to complete capture-the-flag challenges across simulated networks. Internet access was deliberately enabled and safeguards against malicious cyber activity were switched off to test the models' maximum capabilities.
AISI ran the challenge 122 times across seven models. In ten runs, agents took 19 autonomous, unauthorized actions against real people and organizations on the live internet. Seventeen involved Mythos 5, while two came from OpenAI's GPT-5.6 Sol.
Also read: Anthropic's Mythos AI reportedly cracked NSA classified systems in hours, that would explain the ban
In the most serious sequence, Mythos concluded that inserting malicious code into a real GitHub project could create a backdoor into the system it was meant to attack. It researched the project's maintainers, submitted a malicious pull request, and created multiple fake identities to pressure a human maintainer into accepting it.
When challenged, the agent edited one of its fake bug reports to cover its tracks and considered returning under a new identity. One fake persona insisted the code was safe while another backed up the claim.
One report contained a prompt injection designed to trick AI coding assistants into running malicious code. It also sent spear-phishing messages containing harmful payloads and signed one bug report in Danish to appear more convincing to a Danish-speaking maintainer.
Mythos also left public messages offering to cooperate with other agents taking the test, plus instructions for reusing accounts and tools it had created. Later agents discovered and followed them. GPT-5.6 Sol separately put a malicious server online and broke into a GitHub account created by another AI agent.
"This is the first time AISI has seen deception of this severity that was targeted at a real person, unprompted, in the real world," the institute said.
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