Microsoft Copilot for Word Can Copy Hidden Prompts Into New Documents
Microsoft 365 Copilot can rewrite figures in a report using hidden instructions in a Word document and then replicate the same instructions into the final file. On July 28, 144 days after disclosing the method to Microsoft, Håkon Måløy revealed it.
When the internally created file was used in a second Copilot drafting session during his proof of concept, it caused the identical effect.
Microsoft confirmed the observed behavior on March 31 and implemented two mitigations, according to Måløy's chronology. While the second improved the underlying model to GPT-5.5, the first blocked the original prompt phrasing.
He claimed that the attack class continued to replicate on July 28 and that the entire chain functioned with altered instructions on GPT-5.6 the following day. "The vulnerabi...