Hi Skip,

Welcome to Microsoft Community.

I'm Hahn and I'm here to help you with your concern.

I'm sorry to hear that you have a malware problem. The Windows Defender Security Notification that is locking up your computer is a scam that tries to trick you into calling a fake customer support number. You should not call the number or follow any instructions from the scammers. Instead, you should try to remove the malware from your computer as soon as possible.

• Restart in Safe Mode: Restart your computer in Safe Mode to prevent any third-party applications, including malware, from running. Start your PC in safe mode in Windows - Microsoft Support
• Perform a Full Scan with Windows Defender:
  • While in Safe Mode, run a full scan using Windows Defender to identify and remove any malware. To do this, follow these steps: Remove malware from your Windows PC - Microsoft Support
• As a last resort, you may need to do a clean reinstall of Windows to fully remove persistent malware. Be sure to back up any important data first.
• Avoid dubious downloads, email attachments and websites in the future to prevent malware infections. Use a reputable antivirus program and keep it updated.

Let me know if the malware persists after trying some of these steps. Being locked out by a fake security notification is frustrating, but with some effort you should be able to clean it up and regain access to your computer.

Your Sincerely

Hahn - MSFT | Microsoft Community Support Specialist