Microsoft’s Copilot “Reprompt” Hack: AI’s Sneaky Data Leak Nightmare
Security researchers at Varonis just exposed a wild flaw in Microsoft’s Copilot Personal app, letting hackers silently siphon your files, location, chats, and account info through a phishing trick called “Reprompt.” Microsoft patched it in their January Patch Tuesday drop after the team flagged it back in August 2025, but not before proving how easy it was to bypass the AI’s basic guards.
The Gory Details
Here’s how it went down: Victim clicks a malicious phishing link that feeds the AI an initial prompt. Then, the attacker sneaks in follow-up instructions—like “summarize my docs” or “grab my location”—and Copilot happily complies, exfiltrating data without raising alarms. This hit the free Personal version hard; the Enterprise Microsoft 365 Copilot dodged it thanks to beefier controls. No real-world exploits spotted yet, but the proof-of-concept from Varonis Threat Labs showed it working on demand. Key versions? Whatever shipped before January 2026 patches—update now if you’re lagging.
Why Devs Should Sweat This
If you’re building or integrating AI tools, this is your wake-up call. Prompt engineering isn’t just fluff; it’s a battlefield. One weak link in your LLM chain means attackers can jailbreak it for data grabs, turning your fancy Copilot sidebar into a hacker’s backdoor. As a dev, audit your AI inputs, enforce strict prompt validation, and push for enterprise-grade guardrails. This bug proves personal AI apps are soft targets—your side projects or client apps could be next if you’re not hardening prompts against reprompt chains.
Final Take
AI’s power comes with prompt-sized holes; plug ’em fast or watch your data walk. Devs, treat every AI like it’s already compromised—because one day, it will be.
