A security researcher has shown how a prompt injection attack in Microsoft Copilot for Word can spread on its own. Håkon Måløy describes a worm-like attack: an attacker hides instructions in a document using white text on white background at tiny font size. Readers can't see it but Copilot can, since it strips color and font size before processing. When someone uses that document as a source, Copilot runs the hidden instructions and copies them into the new file. That file becomes a carrier. Use it as a template, and the attack fires again. A compromised market analysis from the internet could manipulate a financial report, which then infects further reports.
Microsoft confirmed the behavior on March 31. Two fix attempts failed. After 144 days, Måløy published his findings with no fix in place, though he's holding back the payload text. AI researcher Andreas Kirsch recently joked he wished someone would build exactly this worm to convince skeptics that AI security risks are real. Now it exists. Prompt injections remain an unsolved AI security problem.
