Fix Windows Defender Error 0x800106ba

Windows Defender error 0x800106ba usually appears when the security service fails to start, often after a system update, a third-party antivirus conflict, or corrupted service settings. This guide walks you through the most reliable fixes, from restarting the service to repairing system files, so you can get real-time protection back.

What You’ll Need

• Administrator access to your Windows PC (you’ll need to approve User Account Control prompts).
• A stable internet connection for downloading updates or running online scans.
• About 15–30 minutes of time, depending on which fix you need.

Step-by-Step

1. Restart the Windows Defender Service

1. Press Windows + R, type services.msc, and press Enter.
2. Scroll down to Windows Defender Antivirus Service (or Security Center on some versions).
3. Right-click it and select Restart. If it’s not running, select Start.
4. Set its startup type to Automatic by right-clicking → Properties → Startup type → Automatic → Apply.
5. Close the window and try opening Windows Security again.

2. Run the Built-in Troubleshooter

1. Go to Settings (Windows + I) → System → Troubleshoot → Other troubleshooters.
2. Find Windows Update and run it. Also run System Maintenance if available.
3. Restart your PC after the troubleshooter completes.

3. Check for Conflicting Antivirus Software

1. Open Settings → Apps → Installed apps.
2. Look for any third-party antivirus (e.g., Norton, McAfee, Avast, AVG, Bitdefender).
3. If one is installed, either uninstall it or disable its real-time protection temporarily (check its own settings).
4. Restart and see if Defender starts working.

4. Repair System Files with SFC and DISM

1. Open Command Prompt as administrator: right-click the Start button → Terminal (Admin) or Command Prompt (Admin).
2. Type sfc /scannow and press Enter. Wait for it to finish (may take 10–15 minutes).
3. If errors are found, run DISM /Online /Cleanup-Image /RestoreHealth and press Enter.
4. Restart your PC after both commands complete.

5. Update Windows

1. Go to Settings → Windows Update → Check for updates.
2. Install any pending updates, including optional ones.
3. Restart your PC.

6. Reset Windows Security App

1. Go to Settings → Apps → Installed apps.
2. Search for Windows Security.
3. Click the three dots (⋯) → Advanced options → Reset.
4. Confirm and restart.

7. Use PowerShell to Re-register Defender

1. Open PowerShell as administrator (right-click Start → Terminal (Admin)).
2. Run this command and press Enter:
   Get-AppxPackage Microsoft.Windows.SecHealthUI | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}
3. Wait for it to complete, then restart.

8. Check Group Policy (Pro/Enterprise only)

1. Press Windows + R, type gpedit.msc, and press Enter.
2. Navigate to Computer Configuration → Administrative Templates → Windows Components → Microsoft Defender Antivirus.
3. Double-click Turn off Microsoft Defender Antivirus.
4. Set it to Not Configured and click OK.
5. Restart.

9. Perform a Clean Boot

1. Press Windows + R, type msconfig, and press Enter.
2. Go to the Services tab, check Hide all Microsoft services, then click Disable all.
3. Go to the Startup tab → Open Task Manager → disable all startup items.
4. Restart and check if Defender works. If yes, re-enable services one by one to find the culprit.

Common Mistakes

• Skipping the restart after each step – many fixes only take effect after a reboot.
• Not running Command Prompt as administrator – SFC and DISM will fail without admin rights.
• Leaving a third-party antivirus installed – even if it’s not active, its drivers can block Defender.
• Assuming the error is gone after one attempt – sometimes you need to combine steps 4 and 5.
• Ignoring Windows Update – a pending update can cause the service to fail.

Tips

• Always create a system restore point before making major changes (search “Create a restore point” in Start).
• If you use a third-party antivirus, consider uninstalling it properly with the vendor’s removal tool, not just via Settings.
• Keep Windows Update set to automatic to avoid missing security patches.
• If you’re on a work PC, check with your IT department – Group Policy may be enforcing the error.

Troubleshooting

If the error persists after all steps:

• Try an offline scan – open Windows Security (if possible) → Virus & threat protection → Scan options → Microsoft Defender Offline Scan. This can remove malware that’s causing the service to crash.
• Check the Event Viewer – search “Event Viewer” → Windows Logs → System, look for errors related to Defender or SecurityCenter around the time the error appears. The details can point to the exact cause.
• Use System Restore – if the error started recently, restore your PC to a point before it began.
• Reset Windows – as a last resort, go to Settings → System → Recovery → Reset this PC. Choose “Keep my files” to avoid data loss.
• If nothing works – you may need to reinstall Windows completely. Back up your data first.

Frequently Asked Questions

What causes error 0x800106ba?

It’s typically caused by the Windows Defender Antivirus service not starting, often due to a recent update, a conflicting third-party antivirus, corrupted system files, or incorrect Group Policy settings.

Will I lose my files if I reset Windows Security?

No, resetting the Windows Security app only clears its settings and temporary data. Your personal files are unaffected.

Can I fix this error without admin access?

No, all the fixes require administrator privileges because they modify system services and files. If you’re on a managed device, contact your IT administrator.

Is it safe to use my PC while Defender is not working?

It’s risky. Without real-time protection, your system is more vulnerable to malware. Try to fix the issue as soon as possible, and avoid downloading or opening suspicious files in the meantime.

How long does SFC /scannow take?

It usually takes 10–15 minutes, but it can be longer on older hard drives. Let it finish completely – don’t close the window.

Will this error affect my other apps?

No, the error is specific to Windows Defender. Other applications should work normally, but you may see security warnings until it’s fixed.

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