There is a good chance you are paying for an endpoint security tool you have never turned on.
Most organizations running Business Premium, E3 or E5 already have Microsoft Defender included in their licensing, yet many run CrowdStrike or SentinelOne and leave the Defender entitlement sitting unused in their tenant. This usually traces back to a long standing assumption that two endpoint tools should never run on the same machine.
That assumption does not apply to Defender in passive mode. Passive mode allows Defender to coexist with your existing EDR, so you keep the tool you trust while gaining threat and vulnerability management, phishing detection, endpoint DLP, and Defender XDR telemetry from a license you already own.
Passive mode is a state where Microsoft Defender runs alongside a third-party antivirus without taking over active protection. Your primary EDR keeps handling real-time scanning and quarantine, while Defender stays in the background collecting telemetry and enabling the value added features tied to Defender for Business on Business Premium or Defender for Endpoint on E3 and E5. It matters because it turns a license you are already paying for into an active layer of visibility.
In this episode of the Demystifying Microsoft podcast, host Nathan Taylor sits down with Nick Ross, CEO of CloudCapsule, Microsoft MVP, and the creator behind the T-Minus 365 YouTube channel. The two dig into why passive mode is one of the most underused scenarios in the Microsoft security stack, where it fits for both SMB and enterprise, and how it connects to the bigger shift toward AI-driven security and data governance.
The most common reason is that you already trust another EDR. Teams run CrowdStrike or SentinelOne because they know it, it is fully configured, and it scales cleanly across many tenants with a single console. In the MSP world especially, the biggest knock on Defender has always been that it is harder to manage multi-tenant and at scale, so providers standardize on tools built for that.
Passive mode lets you keep that investment while still capturing the parts of Defender that add value. You get a second set of detection algorithms watching for blind spots, and you unlock features that your third-party tool may not offer at all. There is an old line in security that defender thinks in checklists and attackers think in graphs. Microsoft's security story is built around that attack graph, correlating signals from email, endpoint, and identity to flag a likely breach, and Defender on the endpoint feeds that correlation.
Passive mode is not full protection, and it helps to be clear about the trade. You do not get real-time scanning, file block and quarantine, or scheduled scans, since your primary EDR owns those. What you do get is a strong visibility and signal layer.
Here is what passive mode gives you access to.
Threat and vulnerability management that analyzes the software and OS layer and surfaces CVEs, public exploits, and patch priorities
EDR telemetry feeding Defender XDR and Security Copilot, which matters because AI-driven detection is only as good as the data behind it
SmartScreen phishing detection, where Microsoft sees both the login attempt and the endpoint to catch man in the middle attacks
Endpoint DLP through Purview, since its underlying sensor is Defender itself
Web content filtering that can help you retire a separate tool
Threat intelligence updates and attack surface reduction signals for auditing
Behavior analysis and AI detection, along with optional EDR block mode
These are visibility and signal features, not active enforcement. Your primary EDR still handles prevention, which is where the distinction between passive mode and block mode comes in.
The naming trips people up, since it sounds like a contradiction at first. In plain terms, passive mode means Defender observes and reports while your primary EDR does the enforcing. EDR block mode adds a safety net on top, so if your primary tool analyzes an event and decides it is clean, Defender can still step in at the end of that funnel and block a threat it considers malicious.
Block mode is a useful failsafe, but it carries a caveat. Running two tools that can both take action raises the odds of conflict, and troubleshooting gets harder when an endpoint goes offline and you cannot immediately tell which agent caused it. Passive mode on its own is a low risk deployment in modern environments. Block mode deserves more testing and care before you turn it on broadly.
This is where passive mode gets interesting for teams trying to get AI ready. Because endpoint DLP rides on the Defender sensor, keeping Defender active lets you enforce data protection policies even while another EDR handles endpoint security. You can block cut, copy, and paste into noncompliant locations, and you can stop users from pasting corporate data into tools like DeepSeek or ChatGPT across Chrome and Edge.
A common real word example is insider risk management built on endpoint DLP, tracking signals like data copied to USB drives, mass file deletion or download, and sensitive files sent to a personal Gmail account. All of that telemetry comes from the Defender sensor. It replaces a lot of what teams used to pull only from firewall logs or expensive third-party tooling, and it works for remote and hybrid staff without a VPN in the path.
On endpoints already running a third-party antivirus, Defender usually drops into passive mode automatically once it detects another tool registered with the Windows Security Center. That native behavior is a real win, since two antivirus products fighting over the same machine used to wreck performance.
If you manage devices in Intune, enabling it is as simple as creating a Defender for Business or Defender for Endpoint profile, activating the service, and getting devices enrolled. A best practice worth following is to push the registry key to explicitly set the mode even when auto detection handles it, just in case the tools start stepping on each other.
Yes, Defender supports passive mode on Windows Servers, with one important difference. On servers you have to set the mode explicitly through the registry rather than relying on automatic activation. Server licensing for Defender is genuinely confusing, with standalone options and licensing through Azure Arc or Defender for Cloud, and it shows up far more in enterprise than in SMB.
Even so, the same benefits apply. You get software vulnerability monitoring, CVE telemetry, and visibility into where a server sits in its lifecycle, which is useful when you are planning renewals or migrations. If you are managing servers and want the added visibility, passive mode is a low overhead way to get it.
Treat passive mode as an intentional service rather than something that happens by accident. A few practices keep the deployment clean and low risk.
As Microsoft leans further into E5, E7, zero trust, and AI-driven detection, the value of feeding Defender telemetry into that engine only grows, since more normalized data means better correlation and faster incident response.
Passive mode is one of the easier ways to get more out of licensing you already own, but the details around block mode, exclusions, endpoint DLP, and server configuration are where deployments succeed or stall.
As a Microsoft Solutions Partner with designations for Security and Modern Work, the Sourcepass Center of Excellence for Microsoft can help you scope a pilot, validate it against your current EDR, and confirm you are capturing the telemetry that feeds Defender XDR and Security Copilot.
If you want to see what Defender surfaces in your environment before committing to a full rollout, we can help you plan it.
For more conversations like this one, subscribe to the Demystifying Microsoft podcast so you catch every episode as it drops.