Microsoft defines defense in depth as a security strategy that uses multiple, reinforcing layers of protection to reduce the chance that a single failure leads to compromise. In Microsoft’s security guidance, defense in depth is described as employing “a series of mechanisms across multiple layers” to protect identities, endpoints, applications, data, and the network. The model spans layers such as identity, perimeter, network, compute, application, and data, with controls at each layer designed to detect, prevent, and contain attacks. Typical Azure/Microsoft 365 implementations include identity protections (MFA, Conditional Access), network controls (Azure Firewall, NSGs), perimeter filtering (WAF, DDoS Protection), endpoint safeguards (Defender for Endpoint), application security (code and runtime controls), and data protection (encryption, DLP, Purview Information Protection). By “placing multiple layers of defense throughout a network infrastructure,” an organization limits blast radius and increases resilience if one layer is bypassed. This contrasts with threat modeling (a design-time analysis technique), identity as the security perimeter (a principle of Zero Trust), and the shared responsibility model (a cloud governance concept). The scenario in the question precisely matches Microsoft’s defense in depth methodology.