Researchers Expose Self-Propagating AI Worm in Microsoft Copilot

As generative AI assistants become embedded in Microsoft 365 workflows, prompt injection is evolving from a one-off manipulation technique into a potential propagation mechanism. Researchers found that attackers can conceal malicious instructions inside Word documents and influence Microsoft Copilot when it processes the files. Because the technique does not require macros or conventional malware, it may evade security controls designed to detect executable code and suspicious attachments.

The researchers demonstrated an AI worm that can prompt Copilot to copy hidden instructions into newly created or edited Word files, allowing the payload to spread through ordinary document activity. The attack relies on Copilot interpreting concealed content rather than users running malicious software. As of Aug. 5, 2026, Microsoft had issued mitigation measures, but the researchers said the changes had not fully eliminated the underlying risk of self-propagating prompt injection.