Word Files Spread Malware Through Copilot

A researcher named Hakon Moloy revealed an AI worm that can infect Microsoft Copilot for Word. The worm hides its code using white text on a white background. Humans cannot see it, but Copilot does and runs it. Once executed, the worm changes some financial information or analysis results, and duplicates the code in all subsequent documents generated by the agent.

This attack is performed in two steps. First, an adversary injects code into any document that will be processed by Copilot. When Copilot processes documents, it removes all formatting while keeping the actual content intact. That means the code will run and won’t be visible to the user. Once the worm is executed, the agent duplicates the code in all new documents it generates, creating additional infection points.

This worm can propagate via SharePoint/Teams and doesn’t leave any edits in the history. So, if someone performs a regular audit, they won’t notice this threat. We are dealing with a new type of attack where the AI agent acts as the vehicle for the worm. Instead of opening suspicious attachments from unknown sources, you might get infected by a document within your organization’s network. The researcher reported this issue to Microsoft’s Security Response Center (MSRC) after a collaborative effort that lasted 144 days.