Anthropic has revealed that its Claude AI models breached the systems of three real organisations during a cybersecurity test, after the exercise unexpectedly gained access to the open internet.

The incidents have raised fresh concerns about how advanced AI systems could behave when given greater freedom to operate independently. The tests were designed to take place inside isolated environments, where Claude models were expected to attack simulated targets. However, an operational error gave the systems internet access, allowing them to interact with real-world infrastructure.

Anthropic identified the incidents while reviewing more than 141,000 cybersecurity evaluations conducted with security testing company Irregular. The affected organisations have not been publicly named. The company said two were unaware of the activity until Anthropic contacted them.

The models involved included Claude Opus 4.7, Claude Mythos 5 and an internal research model. During the tests, the AI systems relied on relatively simple methods, such as exploiting weak passwords and unauthenticated access points, to gain entry into vulnerable systems.

Anthropic described the incidents as an operational failure rather than an intentional attack and said it stopped its cyber evaluations on July 23 while investigating what went wrong. The company has also been informing the organisations involved.

The disclosure comes shortly after a separate incident involving OpenAI’s models and adds to growing concerns over AI systems that can independently carry out complex tasks. As companies increasingly use AI agents for coding, security and business operations, controlling what these systems can access has become a major challenge.

The incidents underline the need for stronger safeguards, limited permissions and continuous monitoring when AI systems are connected to real-world networks. As these models become more capable, the line between a controlled security experiment and unintended real-world activity could become increasingly difficult to manage.

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