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Eugene Hill

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Aug 2, 2024, 9:11:15 PM8/2/24

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Microsoft Defender Antivirus is a major component of your next-generation protection in Microsoft Defender for Endpoint. This protection brings together machine learning, big-data analysis, in-depth threat resistance research, and the Microsoft cloud infrastructure to protect devices (or endpoints) in your organization. Microsoft Defender Antivirus is built into Windows, and it works with Microsoft Defender for Endpoint to provide protection on your device and in the cloud.

As a companion to this article, see our Security Analyzer setup guide to review best practices and learn to fortify defenses, improve compliance, and navigate the cybersecurity landscape with confidence. For a customized experience based on your environment, you can access the Security Analyzer automated setup guide in the Microsoft 365 admin center.

Microsoft Defender Antivirus provides anomaly detection, a layer of protection for malware that doesn't fit any predefined pattern. Anomaly detection monitors for process creation events or files that are downloaded from the internet. Through machine learning and cloud-delivered protection, Microsoft Defender Antivirus can stay one step ahead of attackers. Anomaly detection is on by default and can help block attacks such as 3CX Security Alert for Electron Windows App. Microsoft Defender Antivirus started blocking this malware four days before the attack was registered in VirusTotal.

Modern malware requires modern solutions. In 2015, Microsoft Defender Antivirus moved away from using a static signature-based engine to a model that uses predictive technologies such as, machine learning, applied science, and artificial intelligence as this is what's necessary to keep you and your organizations safe from the complexity of today's ever-evolving malware landscape.

We've also designed our antivirus solution to work in both online and offline scenarios. For offline scenarios, the latest dynamic intelligence from the Intelligence Security Graph is provisioned to the endpoint regularly throughout the day. When connected to the cloud, it's fed real-time intelligence from the Intelligent Security Graph.

Microsoft Defender Antivirus can also stop threats based on their behaviors and process trees even when the threat has started execution. A common example of these kinds of attacks is fileless malware. Microsoft's Next-generation protection features work together to identify and block malware based on abnormal behavior. To learn more, see Behavioral blocking and containment.

If you're using a non-Microsoft antivirus/antimalware product on your device, you might be able to run Microsoft Defender Antivirus in passive mode alongside the non-Microsoft antivirus solution. It depends on the operating system used and whether your device is onboarded to Defender for Endpoint. To learn more, see Microsoft Defender Antivirus compatibility.

Beginning with platform version 4.18.2208.0 and later: If a server has been onboarded to Microsoft Defender for Endpoint, the "Turn off Windows Defender" group policy setting will no longer completely disable Windows Defender Antivirus on Windows Server 2012 R2 and later. Instead, it will place it into passive mode. In addition, the tamper protection feature will allow a switch to active mode but not to passive mode.

Note the modified logic for ForceDefenderPassiveMode when tamper protection is enabled: Once Microsoft Defender Antivirus is toggled to active mode, tamper protection will prevent it from going back into passive mode even when ForceDefenderPassiveMode is set to 1.

Passive mode means Microsoft Defender Antivirus running, but is not the primary antivirus/antimalware product on your device. Passive mode is only available for devices that are onboarded to Microsoft Defender for Endpoint and that meet certain requirements. To learn more, see Requirements for Microsoft Defender Antivirus to run in passive mode.

EDR Block Mode means Microsoft Defender Antivirus is running and Endpoint detection and response (EDR) in block mode, a capability in Microsoft Defender for Endpoint, is enabled. Check the ForceDefenderPassiveMode registry key. If its value is 0, it is running in normal mode; otherwise, it is running in passive mode.

Performance tip Due to a variety of factors (examples listed below) Microsoft Defender Antivirus, like other antivirus software, can cause performance issues on endpoint devices. In some cases, you might need to tune the performance of Microsoft Defender Antivirus to alleviate those performance issues. Microsoft's Performance analyzer is a PowerShell command-line tool that helps determine which files, file paths, processes, and file extensions might be causing performance issues; some examples are:

It's important to keep Microsoft Defender Antivirus (or any antivirus/antimalware solution) up to date. Microsoft releases regular updates to help ensure that your devices have the latest technology to protect against new malware and attack techniques. To learn more, see Manage Microsoft Defender Antivirus updates and apply baselines.

If you're using non-Microsoft antivirus/antimalware software, you might be able to run Microsoft Defender Antivirus alongside the other antivirus solution. This article describes what happens with Microsoft Defender Antivirus and non-Microsoft antivirus/antimalware software, with and without Microsoft Defender for Endpoint.

On Windows Server, if you're running a non-Microsoft antivirus product, you can uninstall Microsoft Defender Antivirus by using the following PowerShell cmdlet (as an administrator): Uninstall-WindowsFeature Windows-Defender. Restart your server to finish removing Microsoft Defender Antivirus.On Windows Server 2016, you might see Windows Defender Antivirus instead of Microsoft Defender Antivirus.If you uninstall your non-Microsoft antivirus product, make sure that Microsoft Defender Antivirus is re-enabled. See Re-enable Microsoft Defender Antivirus on Windows Server if it was disabled.

Smart App Control is a consumer-only product that's used on new Windows 11 installs. It can run alongside your antivirus software and block apps that are considered to be malicious or untrusted. Learn more about Smart App Control.

On Windows Server 2019, Windows Server, version 1803 or newer, Windows Server 2016, or Windows Server 2012 R2, Microsoft Defender Antivirus doesn't enter passive mode automatically when you install a non-Microsoft antivirus product. In those cases, set Microsoft Defender Antivirus to passive mode to prevent problems caused by having multiple antivirus products installed on a server. You can set Microsoft Defender Antivirus to passive mode using a registry key as follows:

You can view your protection status in PowerShell by using the command Get-MpComputerStatus. Check the value for AMRunningMode. You should see Normal, Passive, or EDR Block Mode if Microsoft Defender Antivirus is enabled on the endpoint.

Note the modified logic for ForceDefenderPassiveMode when tamper protection is enabled: Once Microsoft Defender Antivirus is set to active mode, tamper protection prevents it from going back into passive mode even when ForceDefenderPassiveMode is set to 1.

On Windows Server 2016, Windows Server 2012 R2, Windows Server version 1803 or newer, Windows Server 2019, and Windows Server 2022, if you're using a non-Microsoft antivirus product on an endpoint that isn't onboarded to Microsoft Defender for Endpoint, disable/uninstall Microsoft Defender Antivirus manually to prevent problems caused by having multiple antivirus products installed on a server. However, Defender for Endpoint includes capabilities that further extend the antivirus protection that is installed on your endpoint. If you have Defender for Endpoint, you can benefit from running Microsoft Defender Antivirus alongside another antivirus solution.

For example, Endpoint detection and response (EDR) in block mode provides added protection from malicious artifacts even if Microsoft Defender Antivirus isn't the primary antivirus product. Such capabilities require Microsoft Defender Antivirus to be installed and running in passive mode or active mode.

Defender for Endpoint affects whether Microsoft Defender Antivirus can run in passive mode. And, the state of Microsoft Defender Antivirus can affect certain capabilities in Defender for Endpoint. For example, real-time protection works when Microsoft Defender Antivirus is in active or passive mode, but not when Microsoft Defender Antivirus is disabled or uninstalled.

a. "Start the scheduled scan only when computer is on but not in use" is set to "Not configured or enabled". A Windows Task Scheduler is created unless you set "Start the scheduled scan only when computer is on but not in use" to disabled.

b. "Turn on catch-up quick scan" is set to "Not configured or enabled". Every 30 days (default number of days) a quick catchup scan continues to occur unless "Turn on catch-up quick scan" is set to disabled. Scan tasks that are set up in Windows Task Scheduler continue to run according to their schedule. If you have scheduled tasks, you can remove them, if preferred.

c. "Turn on scan after security intelligence update" is set to "Not configured or enabled". By default, a quick scan occurs after a "Security Intelligence Update" unless you set "Turn on scan after security intelligence update" to disabled.

When Microsoft Defender Antivirus is in passive mode, it doesn't remediate threats. However, Endpoint detection and response (EDR) in block mode can remediate threats. In this case, you might see alerts showing Microsoft Defender Antivirus as a source, even when Microsoft Defender Antivirus is in passive mode.

The security intelligence update cadence is controlled by Windows Update settings only. Defender-specific update schedulers (daily/weekly at specific time, interval-based) settings only work when Microsoft Defender Antivirus is in active mode. They're ignored in passive mode.