Immediately isolate all affected systems and restrict access to sensitive data without prior analysis, to prevent any potential data breach.

Use Microsoft 365 security tools, such as Microsoft Defender for Office 365 and Microsoft Defender for Cloud Apps, to identify and analyze the threat, then collaborate with legal and compliance teams to ensure any response aligns with regulatory requirements.

Deploy security patches or updates across all systems without assessing the threat's scope, to ensure all potential vulnerabilities are addressed.

Monitor the situation without taking immediate action, to gather more information about the threat's origin and method of operation.

All of the above.