More than 100 major companies have issued an open letter warning that artificial intelligence (AI) is about to significantly change the scale and complexity of cyberattacks. The letter, signed by tech giants like OpenAI, Microsoft, Google, and financial institutions such as Mastercard and Visa, highlights the urgent need for stronger global cyber defenses. The signatories argue that while AI can be a powerful tool for both attackers and defenders, the window to prepare for more advanced threats is limited. The letter explains that AI-powered cyberattacks are becoming more sophisticated and automated. However, it also notes that current AI advancements can help identify and fix security weaknesses that have developed over years. If nations and organizations act with determination, the digital world can be made much safer. The signatories emphasize that proactive measures are critical to prevent large-scale digital offensives from becoming more difficult to counter. In November 2025, Anthropic, one of the signatories, revealed that it had thwarted a major cyberattack likely orchestrated by hackers from China. The attackers used an AI tool called Claude Code Agent to automate up to 90% of the attack. This was the first documented case of such a large-scale AI-driven cyberattack. Following this incident, similar attacks occurred throughout 2026, including the emergence of self-modifying malware, AI-driven evasion techniques, and breaches of AI companies like OpenAI and Anthropic itself. The coalition, led by OpenAI, includes major players across the digital sector, including AI developers, internet providers, cloud services, and industries like banking, telecommunications, and automotive. These companies are particularly concerned about the security of essential services that people rely on daily, such as healthcare systems, water treatment facilities, and the infrastructure that supports the internet. They stress that vulnerabilities in these areas could have serious consequences for public safety and daily life. To address the growing threat, the coalition has proposed a multi-faceted action plan. It calls for using AI to detect and fix security flaws faster than hackers can exploit them. It also urges responsible access to AI models and increased investment in protecting critical infrastructure. Governments are being asked to help fund the cybersecurity efforts of public institutions, such as hospitals, that may lack the necessary resources. Finally, private companies are encouraged to share threat data immediately when cyberattacks are detected, helping to create a more coordinated response to AI-driven cyber threats.