Fix Windows Defender Error 0x80073b01: Complete Guide

Quick Fix

Windows Defender error 0x80073b01 means the security service can’t start properly. To fix it: Open Command Prompt as Administrator, run sfc /scannow, then run DISM /Online /Cleanup-Image /RestoreHealth. Restart your computer and try Windows Defender again. This repairs corrupted system files causing the error.

What Is Windows Defender Error 0x80073b01?

Error code 0x80073b01 appears when Windows Defender (Windows Security) cannot start or function properly. You might see messages like “Windows Defender has encountered a problem” or “Threat service has stopped.” This leaves your computer without real-time protection.

Common causes include corrupted system files, third-party antivirus conflicts, disabled Windows services, group policy restrictions, or malware that has disabled Defender. Let’s fix it.

Method 1: Run SFC and DISM Scans

System file corruption is a common cause of Defender errors.

1. Press Windows + X
2. Select Terminal (Admin) or Command Prompt (Admin)
3. Run: sfc /scannow
4. Wait for completion (may take 10-15 minutes)
5. Run: DISM /Online /Cleanup-Image /RestoreHealth
6. Wait for completion (may take 15-20 minutes)
7. Restart your computer
8. Try opening Windows Security

Method 2: Restart Windows Security Services

Required services may have stopped running.

1. Press Windows + R
2. Type services.msc and press Enter
3. Find and double-click Windows Defender Firewall
4. Set Startup type to Automatic
5. Click Start if the service is stopped
6. Click OK
7. Repeat for these services:
   • Security Center
   • Windows Defender Advanced Threat Protection
   • Microsoft Defender Antivirus Service
8. Restart your computer

Method 3: Remove Third-Party Antivirus

Other security software can conflict with Windows Defender.

1. Go to Settings > Apps > Installed apps
2. Find any third-party antivirus (Norton, McAfee, Avast, AVG, Kaspersky, etc.)
3. Click Uninstall
4. Follow the uninstall wizard
5. Restart your computer
6. Windows Defender should activate automatically

Note: Only one antivirus should be active at a time. Windows Defender automatically disables when third-party antivirus is installed.

Method 4: Check Group Policy Settings

Group Policy may have disabled Windows Defender.

1. Press Windows + R
2. Type gpedit.msc and press Enter
3. Navigate to: Computer Configuration > Administrative Templates > Windows Components > Microsoft Defender Antivirus
4. Double-click “Turn off Microsoft Defender Antivirus”
5. Set it to Not Configured or Disabled
6. Click OK
7. Restart your computer

Note: gpedit.msc is only available on Windows Pro/Enterprise. Home users should use Method 5.

Method 5: Fix Via Registry

Registry settings may be disabling Defender.

1. Press Windows + R
2. Type regedit and press Enter
3. Navigate to: HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
4. Look for DisableAntiSpyware entry
5. If it exists and value is 1, double-click it
6. Change the value to 0
7. Or right-click and delete the entry
8. Restart your computer

Warning: Be careful editing the registry. Back up before making changes.

Method 6: Reset Windows Security App

The Windows Security app itself may be corrupted.

1. Press Windows + I to open Settings
2. Go to Apps > Installed apps
3. Search for Windows Security
4. Click the three dots and select Advanced options
5. Click Repair first
6. If that doesn’t work, click Reset
7. Restart your computer

Method 7: Re-register Windows Defender

Re-registering can fix app registration issues.

1. Open PowerShell as Administrator
2. Run this command:

Get-AppxPackage Microsoft.SecHealthUI -AllUsers | Reset-AppxPackage

3. If that fails, try:

Add-AppxPackage -DisableDevelopmentMode -Register "C:\Windows\SystemApps\Microsoft.Windows.SecHealthUI_cw5n1h2txyewy\AppXManifest.xml"

4. Restart your computer

Method 8: Check for Malware

Malware often disables Windows Defender to avoid detection.

1. Download Malwarebytes from malwarebytes.com
2. Install and run a full scan
3. Remove any threats found
4. Download Microsoft Safety Scanner from Microsoft
5. Run a full scan
6. Restart and check if Defender works

Method 9: Enable Windows Defender via PowerShell

Force-enable Defender using PowerShell commands.

1. Open PowerShell as Administrator
2. Run these commands:

Set-MpPreference -DisableRealtimeMonitoring $false
Start-Service WinDefend
Start-Service WdNisSvc

3. Check Windows Security to see if it’s working

Method 10: Update Windows

Windows updates include Defender fixes and definition updates.

1. Go to Settings > Windows Update
2. Click Check for updates
3. Install all available updates
4. Also check Optional updates for driver updates
5. Restart your computer
6. Try Windows Security again

Method 11: Clean Boot Windows

Third-party software might be interfering with Defender.

1. Press Windows + R, type msconfig, press Enter
2. Go to Services tab
3. Check “Hide all Microsoft services”
4. Click “Disable all”
5. Go to Startup tab
6. Click “Open Task Manager”
7. Disable all startup items
8. Restart your computer
9. Test if Defender works
10. If it works, enable services one by one to find the conflict

Method 12: Repair Windows Installation

If nothing else works, repair your Windows installation.

Using Windows Settings:

1. Go to Settings > System > Recovery
2. Click “Reset this PC”
3. Choose “Keep my files”
4. Follow the prompts to reinstall Windows

Using Installation Media:

1. Create Windows 11 installation USB
2. Boot from USB
3. Choose “Repair your computer”
4. Try Startup Repair
5. Or choose “Reset this PC”

Common Causes of 0x80073b01

• Third-party antivirus not fully removed
• Malware disabling Defender
• Corrupted Windows system files
• Group Policy or registry changes
• Windows Security app corruption
• Disabled Windows services

Preventing Error 0x80073b01

• Use only one antivirus at a time
• Fully uninstall old antivirus before installing new one
• Keep Windows updated
• Don’t disable Windows Defender manually
• Run periodic malware scans
• Don’t use registry cleaners or system “optimizers”

FAQ

What does Windows Defender error 0x80073b01 mean?

Error 0x80073b01 indicates Windows Defender cannot start or function properly. The security service has encountered a problem, often due to corrupted files, conflicting software, disabled services, or malware interference.

Can I use my computer without Windows Defender?

While your computer will function, you’ll have no real-time malware protection. Fix the error as soon as possible, or temporarily install a third-party antivirus. Don’t leave your system unprotected.

Why did my antivirus break Windows Defender?

When you install third-party antivirus, Windows Defender automatically disables to avoid conflicts. If the third-party software is uninstalled improperly, Defender may not re-enable correctly, causing error 0x80073b01.

Can malware cause error 0x80073b01?

Yes, many malware programs specifically target Windows Defender to disable it. If you suspect malware, use Malwarebytes or Microsoft Safety Scanner to scan while Defender is disabled, then fix the Defender error.

Will resetting Windows fix 0x80073b01?

Yes, resetting Windows (keeping your files) will repair Windows Defender along with other system components. It’s a last resort but effective if other methods fail.

How do I know if Windows Defender is working?

Open Windows Security (search for it in Start menu). If it opens without errors and shows green checkmarks for protection areas, Defender is working. You can also check that real-time protection is “On” under Virus & threat protection.