Microsoft Defender Scam or Do I have a virus on my computer

The behavior described matches a common tech support scam, not legitimate Microsoft Defender activity.

What to do immediately

1. Assume the pop-up and phone number were fake
   • Microsoft error or warning messages, including from Microsoft Defender, never include a phone number to call.
   • Microsoft does not make unsolicited support calls or ask to be called from random pop-ups.
2. If any software or remote-access tool was installed
   • Uninstall any applications that the caller asked to be installed.
   • Consider resetting the device to factory state if any remote access or unknown tools were used.
3. Scan the device
   • Run a full scan with Microsoft Defender Antivirus and install all available security updates.
4. Protect accounts and data
   • Change passwords for important accounts (email, banking, Microsoft account, etc.).
   • Monitor for unusual sign-in activity or suspicious account behavior.
   • If any payment was made, contact the bank or card provider and explain that it may have been a scam.
5. Close and clear the browser if it happens again
   • If the browser is locked with a similar message, close it using:
     • Alt + F4 to close the window, or
     • Ctrl + Shift + Escape → Task Manager → end the browser process, or
     • Restart or power off the computer if needed.
   • Afterward, clear the browser cache.
6. Reporting and getting legitimate help
   • Report the scam to Microsoft at https://www.microsoft.com/reportascam.
   • For urgent help, contact Microsoft only through official support channels such as the Microsoft Support site or the published Global Customer Service phone numbers.
   • Local law enforcement can also be notified if money or sensitive data was taken.

How to reduce risk going forward

• Do not call phone numbers shown in pop-ups or “Defender” alerts.
• Do not trust unsolicited calls or emails offering to fix a device.
• Download software only from official vendor sites or the Microsoft Store.
• Use Microsoft Edge with Microsoft Defender SmartScreen enabled to help block known scam sites.

Whether the computer is infected depends on what the scammer had done on the device. Following the steps above (uninstalling anything they added, running a full Defender scan, changing passwords, and monitoring accounts) is the recommended next action.

References:

• Protect yourself from online scams and attacks
• Protect yourself from tech support scams
• Tech support scams
• My computer was locked by Microsoft defender, I was asked to call 1-844-452-2441 to get it unblocked. Could somebody confirm that this is a legitimated Microsoft number rather than a scammer? - Microsoft Q&A
• possible virus, computer locked - Microsoft Q&A