How to Turn on Windows Defender

Turn on Microsoft Defender

You need to make sure that Microsoft Defender has been turned off recently. If you have disabled Microsoft Defender between the last restart/shutdown and now, Microsoft Defender may not be working again. You can reactivate with the following steps.

If you have not turned off Microsoft Defender since the last time you restarted your computer, it is possible that Microsoft Defender is disabled by another new antivirus program. You need to uninstall this antivirus program to reactivate Windows Defender.

Open Start . Click the Windows logo in the lower left corner of the screen.

Open Settings. Click the gear icon in the lower left corner of the Start menu. The Settings window will open.

Click Update & Security. This option with a circular arrow icon is in the Settings window.

Click the Windows Security tab . It's on the left side of the screen.

Click Virus & threat protection. This option is in the middle of the window.

You may need to expand the Windows Security window by clicking the square in the upper-right corner of the window before continuing.

Click Virus & threat protection settings . This link is in the middle of the menu.

Click the "Off" switch below the "Real-time protection" heading. This title is near the top of the window.

Click Yes when prompted. Microsoft Defender will be turned back on.

Uninstall third-party anti-virus programs

Determine if you have recently actively installed any other anti-virus programs. If so, this is the reason why Windows Defender is disabled. If not, it's likely that another antivirus program was automatically installed by some software as part of the package. In this case, you need to find the 'culprit' even though the name is unknown.

Open Start . Click the Windows logo in the lower left corner of the screen.

Open Settings . Click the gear icon in the lower left corner of the Start menu. The Settings window will open.

Click the Apps option . It's in the middle of the Settings window.

Sort programs by date (if necessary). If you're not sure which anti-virus program is which, you can narrow your search by checking the most recently installed programs. To proceed, click "Sort by" and then select Install date from the drop-down menu.

If you already know the name of the anti-virus program, you can skip this step.

Find an anti-virus program. Scroll through the list of installed applications until you find the program you need to remove.

If you haven't actively installed any anti-virus programs recently, the 'culprit' may be near the top of the application list if Windows Defender has only recently been turned off.

Click on the name of the program to uninstall. The program name will expand and an Uninstall button will appear .

Click the Uninstall button located below the program name.

Click Uninstall when prompted. The program uninstallation window will open.

Follow the uninstallation instructions. Click through the uninstall prompts that appear on the screen. Additionally, check to make sure the "Delete all files" option (or similar) is selected if the process asks you if you want to keep leftover files and applications.

Delete the related program. Some antivirus programs come with additional programs to handle things like web security. So, if you find a program that comes from the same developer or has a similar name to the antivirus software you just removed, uninstall it before continuing.

Restart the computer. Click the Start button , select Power , and click Restart in the pop-up menu. After the computer restarts normally, Windows Defender will be back up and running.

If Microsoft Defender doesn't run automatically after your computer restarts, you can turn it on manually.