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Defending the Inbox Against Prompt Injection Attacks
Publication date not yet evaluated · Added microsoft.com
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Single-source advisory — one report is available.
Why it matters
Microsoft's new Defender prompt-injection filtering signals that email has become an attack surface against AI assistants, where hidden instructions can trigger data exposure or unauthorized tool calls without any human click.
Microsoft announced a new Microsoft Defender for Office 365 capability that detects and quarantines malicious AI instructions (prompt injection) embedded in email before delivery, aiming to stop indirect prompt injection from reaching Copilot and Microsoft 365 agents. The post cites publicly disclosed research such as Morris II and EchoLeak as evidence that email is a high-volume ingress channel for AI-targeted attacks, describing techniques like white-on-white text, zero-width Unicode, and hidden HTML instructions.