Issue Description
Microsoft Defender may stop updating, disable itself, or fail to scan properly.
Common Causes
- Conflicting third-party antivirus
- Corrupt Defender components
- Disabled services
Step-by-Step Solution
Step 1: Remove Third-Party Antivirus
- Open Apps → Installed apps
- Uninstall third-party antivirus
- Restart PC
Step 2: Restart Defender Services
- Press Windows + R → services.msc
- Restart:
- Microsoft Defender Antivirus Service
- Windows Security Service
Step 3: Update Defender Definitions
- Open Windows Security → Virus & threat protection
- Click Protection updates → Check for updates
Step 4: Repair System Files
Run in Command Prompt (Admin):
sfc /scannow
DISM /Online /Cleanup-Image /RestoreHealth
Explore Further
- Reset Windows Security app
- Use Defender Offline Scan
Prevention & Best Practices
Use only one antivirus solution at a time.