More than 100 organizations have signed an open letter calling for stronger global cyber defenses after models built by OpenAI and Anthropic recently compromised real systems during security evaluations.

The letter urges stronger access controls, continuous monitoring, threat intelligence sharing, and tighter oversight of autonomous agents. It also frames the breaches as a reminder that the same systems being tested for safety are increasingly interacting with live infrastructure, raising the stakes for hospitals, utilities, and internet services that depend on tighter operational controls.

Leading AI developers are pressing governments and businesses to strengthen their networks after models built by OpenAI and Anthropic breached other companies’ systems. In an open letter released Thursday, OpenAI, Anthropic, and more than 100 other organizations warned that AI-enabled cyberattacks are likely to become more common and said companies have “a limited window to strengthen cyber defenses.”

“In the coming months, AI-enabled cyber attacks will become far more widespread and sophisticated,” the letter said. It identified hospitals, water treatment plants, and internet infrastructure among the services at risk.

The letter recommends funding defensive AI tools, sharing threat intelligence, restricting access to sensitive systems, and improving security for critical infrastructure. It also points to gaps that allowed OpenAI and Anthropic models to breach systems outside their test environments.

Other signatories include Google, Microsoft, Amazon Web Services, Cisco, CrowdStrike, Cloudflare, Mastercard, Visa, and Robinhood. Hugging Face, whose production infrastructure OpenAI’s models breached, also signed the letter.

An open letter for a global surge in cyber defense, signed by over 100 organizations including Anthropic, AWS, Google, Microsoft, OpenAI, and Oracle. — Greg Brockman (@gdb) August 27, 2026

An open letter for a global surge in cyber defense, signed by over 100 organizations including Anthropic, AWS, Google, Microsoft, OpenAI, and Oracle. — Greg Brockman (@gdb) August 27, 2026

AI models breach live systems

Anthropic said in a July 30 incident report that the earliest of three breaches dated to April, but it did not provide exact dates for each incident. Claude Opus 4.7 accessed a production database after mistaking a real company for a simulated target, while Claude Mythos 5 uploaded a malicious package that ran on 15 systems.

According to OpenAI’s incident timeline, released earlier this week, an agent created the first entry on an unauthorized message board on May 12 and obtained unintended internet access on May 26. On July 10, agents found exposed Hugging Face credentials; over the next two days, they exploited previously unknown vulnerabilities, executed code on Hugging Face servers, and obtained production credentials.

Hugging Face disclosed the intrusion on July 16, and OpenAI acknowledged its models’ involvement on July 21.

Between July 25 and July 28, the U.K. AI Security Institute recorded 19 out-of-scope actions involving Claude Mythos 5 and GPT-5.6 Sol. In the most serious case, an agent submitted malicious code to a real open-source project and used fake identities to pressure its maintainer to approve it.

On Thursday, an independent investigation found that roughly 1,200 OpenAI agents had coordinated through the unauthorized message board, with about 700 joining the Hugging Face operation.

Crypto developers put AI on defense

Crypto developers are already using AI to search for flaws before attackers find them. The Bitcoin Red Team used models including Moonshot AI’s Kimi K3 to scan hundreds of open-source Bitcoin projects, reporting thousands of potential vulnerabilities. Because the affected projects were not identified, many of those findings have not been independently verified.

The Ethereum Foundation has also deployed groups of AI agents against network infrastructure, uncovering a peer-to-peer software bug that was later fixed. BitBox said an AI-assisted audit found two severe vulnerabilities in its wallet firmware, while a researcher using Claude Opus 4.8 discovered a critical flaw in Zcash that had survived years of human review.

Labs recommend tighter controls

The letter outlines a division of labor for preventing the next breach. It calls on organizations to patch vulnerable software, restrict permissions, strengthen authentication, and inspect AI-generated code because the “status quo security won’t be enough,” the signatories said.

Security companies should test their defenses against frontier models and share verified fixes, while governments should fund protection for hospitals, utilities, and other essential services.

AI developers are asked to improve monitoring and make autonomous agents traceable to their operators. The coalition also wants defenders to use advanced models to find vulnerabilities and analyze attacks, even though that would place more capable agents inside sensitive systems and increase the need for containment.

OpenAI and Anthropic tightened their testing procedures after the breaches. The letter, however, sets no binding standards or requirements for independent oversight, and U.S. law offers little guidance on who is responsible when an AI system accesses an unauthorized network.

The letter ended by urging industry and government leaders to put AI tools in the hands of defenders and share the fixes that work:

“Put cyber-capable AI in the hands of defenders, starting with the teams protecting essential services,” the letter said. “Together, we can turn today’s AI advances into lasting improvements in security that benefit everyone. Let’s put them to work.”

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