Forensic Summary
Microsoft's September 2026 security update delivers network-layer data loss prevention for agentic AI traffic, AI-generated email detonation summaries in Security Copilot, and enterprise-scale labelling automation in Microsoft Purview. These capabilities close a material gap for defenders by extending Zero Trust policy enforcement to on-behalf-of (OBO) agent actions — an emerging blind spot as autonomous agents operate across employee devices and cloud platforms. Residual gaps remain around coverage breadth for third-party agent frameworks, cross-platform policy portability, and the organisational maturity required to define reliable classification policies before enforcement becomes effective.
Read the full technical deep-dive on Grid the Grey: https://gridthegrey.com/posts/microsoft-defender-and-purview-add-ai-agent-controls-in-september-2026/
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