A security researcher built a self-spreading worm that hides inside Word docs and hijacks Microsoft Copilot
144 days. Microsoft still hasn't patched a self-spreading worm that hijacks Copilot through Word documents.
Why it matters
A demonstrated agent exploit — invisible prompt injections that propagate across documents and compromise Copilot's autonomy — exposes a critical reliability and security gap in deployed agentic systems. This is the kind of failure mode that will determine whether agents scale in enterprise.
The key facts
6 to knowSelf-spreading worm embeds invisible prompt injections in Word documents
Injections automatically propagate to new files on document reuse
Microsoft acknowledged the vulnerability but failed to patch after 144 days
Two patch attempts by Microsoft were unsuccessful
Attack specifically targets Microsoft Copilot for Word — an agent-adjacent product
Security researcher demonstrated and disclosed the issue
Go to the source
The Decoderthe-decoder.com
Publisher excerpt: A security researcher has demonstrated a worm-like attack on Microsoft Copilot for Word: invisible prompt injections hidden in documents spread automatically into new files every time they're reused. Microsoft confirmed the issue but failed to fix it after 144 days and two attempts.