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If Microsoft Defender Antivirus looks turned off after Windows Update, first check which antivirus provider Windows Security lists as protecting your PC. A compatible non-Microsoft antivirus product can automatically put Defender into disabled mode; the timing alone does not prove that Windows Update caused the change. If no other provider is active, check Real-time protection and then confirm that security intelligence is up to date.
Why is Microsoft Defender turned off after Windows Update?
The most common explanation documented by Microsoft is that another compatible antivirus product is active. Microsoft says that when such a product is in use, Microsoft Defender Antivirus automatically turns off or enters disabled mode. Windows Update may have happened around the same time, but that timing does not establish that the update caused Defender’s status.
Windows Security also distinguishes between antivirus protection being off and security intelligence being out of date. Check the provider and protection setting first; investigate updates separately if protection is on but definitions are stale or failing to update.
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- Open Windows Security.
- Select Virus & threat protection.
- Under Who’s protecting me?, select Manage providers.
- Check the antivirus provider Windows lists as active.
If a compatible third-party antivirus is active and you intend to keep using it, Defender being disabled may be expected. Microsoft says Defender should return to active mode automatically after the other antimalware software is uninstalled. Avoid trying to run two antivirus products at once as a default fix: Microsoft warns that multiple products can cause performance or stability problems. Microsoft’s provider-check instructions and its guidance on protecting a PC from viruses explain these behaviors.
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How do I turn Microsoft Defender Antivirus back on?
If no other antivirus provider is responsible, check the built-in Real-time protection setting:
- Open Windows Security.
- Go to Virus & threat protection > Manage settings.
- Turn on Real-time protection.
Real-time protection may be switched off temporarily and can turn itself back on automatically later. While it is off, files you open or download are not checked by real-time protection. Microsoft documents the setting and its behavior in Virus and threat protection in the Windows Security app.
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What if Defender is on but security intelligence will not update?
Security intelligence updates are separate from the provider status and Real-time protection toggle. Windows downloads them through Windows Update, and you can also check for updates manually. If Defender repeatedly reports errors while updating protection, Microsoft recommends trying to install the latest protection updates manually. See Microsoft’s malware detection and removal troubleshooting guidance.
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Tamper protection helps prevent apps from changing Windows Security settings. Microsoft says an administrator can still change settings in Windows Security when tamper protection is on, while other apps cannot. If Real-time protection is unavailable, switches off repeatedly, or the PC belongs to an employer or school, check whether the device is managed and contact its administrator or Microsoft Support.
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Do not disable tamper protection, edit registry values, or force Defender services to start as a workaround. Those steps can bypass protections or conflict with device management rather than resolve the cause.
Does the Windows 10 security troubleshooter still apply?
Microsoft lists an automatic Windows Security troubleshooter for Windows 10 that checks settings including antivirus status and updates. Treat it as a legacy option if it is still available, not the first-line fix for every PC: Microsoft notes that the Microsoft Support Diagnostic Tool (MSDT) is deprecated, and Windows 10 support ended on October 14, 2025. Microsoft’s Windows security troubleshooter page describes its scope and limitations. For Windows 10, do not assume free security fixes will continue through Windows Update after the end of support; check Microsoft’s Windows Security and support information for your situation.
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When should I escalate the problem?
Contact Microsoft Support or your organization’s IT support if Real-time protection cannot be enabled, Defender remains inactive after the other antivirus product has been removed, or device management prevents you from changing the setting. When asking for help, note your Windows version, the provider shown in Manage providers, the exact warning or error code, whether the PC is managed by work or school, and whether security intelligence updates succeed.
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