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Word worm crawls into Copilot, spreads chaos

Håkon Møløy said Microsoft’s fixes have not closed the flaw after 144 days, and a malicious Word file can still spread through Copilot workflows.

  • 144 days after a researcher warned Microsoft, a document-borne AI-worm still functions, allowing attackers to manipulate Copilot by embedding hidden text within Word documents.
  • Copilot treats document content as prompts, creating a vulnerability where hidden instructions manipulate output; asking a model to evaluate untrusted code just leads to "LLMs all the way down."
  • Microsoft attempted to mitigate the issue by blocking specific prompts and upgrading to GPT-5, but attackers simply reworded the payload, rendering both fixes ineffective.
  • Pointing to a defense-in-depth strategy blocking malicious instructions "at multiple points," the company acknowledged that "prompting alone is not a reliable security boundary."
  • Satya Nadella confirmed a Copilot "super app" launching this year with revenue up 60%, while SecurityWeek reported similar "hallusquatting" risks from Tel Aviv University and Intuit researchers.
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In the world of advanced technology, security vulnerabilities stand out as serious threats. In this article, we examine a new vulnerability in Microsoft Copilot for Word, where hidden instructions can compromise document integrity. The leakage of hidden instructions in Word documents by Microsoft Copilot can cause the hidden instructions in a Microsoft 365 Word document to rewrite numbers in a report and then copy the same instructions to the fi…

A security researcher has demonstrated that a Word trapped document can contaminate all the files generated by Copilot, and spread from document to document, without intervention by the attacker. 144 days of coordination with Microsoft, two attempts to fix, an upgrade to the underlying IA model. And

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The Register broke the news in London, United Kingdom on Wednesday, July 29, 2026.
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