What is Microsoft Defender for Identity (MDI) and what does ITDR mean?
Microsoft Defender for Identity (formerly Azure Advanced Threat Protection) is the Microsoft Identity Threat Detection and Response (ITDR) product. ITDR is the security industry category for behavior-based detection of identity-layer attacks — credential theft, ticket forgery, lateral movement, privilege escalation, and federation abuse — across both on-premises Active Directory and cloud identity (Entra ID). MDI deploys lightweight sensors directly on writable domain controllers, AD FS federation servers, and AD CS certificate authorities, then correlates the captured signal with Entra ID Protection and the rest of the Microsoft Defender XDR platform. The result is identity-layer detection that complements endpoint-layer EDR with the directory-aware signal an EDR alone cannot produce.
How does Microsoft Defender for Identity compare to CrowdStrike Falcon Identity Protection?
MDI and CrowdStrike Falcon Identity Protection are the two leading ITDR products. MDI wins on bundled value (already paid for inside Microsoft 365 E5 and E5 Security), on tight integration with Entra ID Protection and Defender XDR, and on AD CS certificate-template abuse detection through the dedicated AD CS sensor. CrowdStrike wins on agent-based identity monitoring that does not require sensor placement on every DC, on the Falcon Identity Protection console for IdP-agnostic deployments, and on threat intelligence breadth from the CrowdStrike Intelligence team. For Microsoft-anchored enterprises that own E5, MDI is the rational choice because the activation cost is deployment services only. For multi-EDR environments or environments where CrowdStrike Falcon is already the endpoint platform of record, Falcon Identity Protection can simplify operations by consolidating on one vendor.
How does Microsoft Defender for Identity compare to Tenable Identity Exposure (formerly Tenable.ad)?
Tenable Identity Exposure is a posture and exposure management product for Active Directory and Entra ID, where MDI is a detection and response product. The two are complementary rather than competitive. Tenable Identity Exposure excels at continuous exposure assessment — finding misconfigurations, exposed credentials, weak ACLs, dangerous trust paths, and the BloodHound-style attack-path analysis that helps proactively close exposure before an attacker exploits it. MDI excels at runtime detection — observing the Kerberos and Netlogon traffic for actual attack behavior. EPC Group sees the strongest defensive posture from running both: Tenable Identity Exposure for continuous attack-path closure, MDI for runtime detection and Defender XDR fusion when an attack does occur.
What is the MDI sensor deployment model, and how does it affect domain controller performance?
The modern MDI deployment model uses a single sensor type installed directly as a Windows service on writable domain controllers, AD FS servers, and AD CS certificate authorities — the older standalone-sensor model with port mirroring is deprecated. The sensor reads ETW providers, the directory replication stream, and the relevant Kerberos and Netlogon traffic directly through the local network stack. Microsoft validates the sensor at under 1 percent CPU and under 350 MB memory on properly sized hardware, which is well within the headroom of any DC sized to handle the directory load. EPC Group runs a controlled rollout against a pilot DC pair first, captures baseline performance metrics, validates impact, and then broad-rolls under change control. We have never seen the sensor cause a production DC issue in any of the deployments we have led when the DC is properly sized to begin with.
What is the difference between Defender for Identity (MDI) and Defender for Office 365 (MDO)?
Defender for Identity (MDI) and Defender for Office 365 (MDO) are two of the five modules inside Microsoft Defender XDR and they protect different parts of the attack surface. MDI protects the identity plane — on-premises Active Directory through sensors on DCs, AD FS, and AD CS, and the hybrid path into Entra ID through Identity Protection correlation. MDO protects the email and collaboration plane — Exchange Online, SharePoint Online, OneDrive, and Microsoft Teams chat — with Safe Attachments, Safe Links, anti-phishing, and Threat Explorer. They share the Defender XDR incident graph, so an attack that starts as a phishing email (MDO detection) and pivots to credential theft and lateral movement (MDI detection) shows up as a single correlated incident with the full timeline.
How does MDI integrate with Microsoft Entra ID Identity Protection and Conditional Access?
MDI sends signal into the Entra ID Identity Protection risk engine — when MDI detects an on-premises Kerberos attack against a hybrid-joined account, the corresponding Entra ID user risk is elevated, which Conditional Access can act on through risk-based policies (force MFA, block sign-in, require password change). The reverse is true as well — Entra ID Protection signal (impossible travel, anonymous IP, leaked credentials) feeds back into MDI investigations through the Defender XDR fusion layer. EPC Group configures the bi-directional integration in every deployment because it is what turns two separate identity products into one unified hybrid identity protection plane. The integration requires Entra ID P2, which is included in Microsoft 365 E5 and E5 Security but not in E3.
What is the difference in scope between Defender XDR and Defender for Identity inside it?
Microsoft Defender XDR is the unified Extended Detection and Response platform that correlates signal across all five Defender modules and Entra ID Protection. Defender for Identity (MDI) is one of those five modules — the identity-layer detection module. Defender XDR is where MDI alerts are investigated, correlated with Endpoint, Cloud Apps, and Office 365 alerts, grouped into incidents, and acted on through attack disruption. MDI is where the actual detection of identity attacks happens — the sensor on the DC, the Kerberos traffic analysis, the directory replication monitoring. Most enterprises that buy Microsoft 365 E5 own both, and the EPC Group recommendation is to activate MDI early in the Defender XDR rollout because the identity plane is where attackers spend most of their time after initial endpoint compromise.
What does an MDI engagement cost, and how long does a full ITDR Accelerator take?
EPC Group delivers full MDI activation under a fixed-fee engagement between $150,000 and $500,000 depending on directory complexity, AD FS and AD CS footprint, Tier 0 hardening scope, regulatory requirements, and managed-service tail. A typical engagement runs eight to fourteen weeks across the five phases (Assess, Activate, Harden, Hunt, Operate). The mid-market engagements (single forest, no AD FS, modest AD CS) cluster near the $150K to $250K end. The complex engagements (multi-forest, federation across regulated subsidiaries, AD CS certificate template remediation, krbtgt rotation under regulatory change control) cluster near the $400K to $500K end. Managed ITDR services are a separate annual subscription priced per protected user with senior-architect escalation included.