Windows Defender protects your Windows computer from malware. If you have deactivated it since the last restart, you can reactivate it from the dedicated program. If you've recently installed an antivirus program that turns off Windows Defender, you'll need to uninstall that program before you can use Windows Defender.
Method 1 of 2: Activate Windows Defender
Step 1. Make sure Windows Defender has been recently disabled
If you've turned off Windows Defender since the last time you restarted or turned off your computer, it should still be turned off. You can reactivate it by following the instructions in this method.
If you haven't turned off Windows Defender since the last time you restarted your computer, chances are it is because of another antivirus program you installed. You will need to uninstall this program before you can reactivate Windows Defender
Step 2. Open the Start menu
Click on the Windows logo at the bottom left of the screen.
Step 3. Go to Settings
Click on the cogwheel icon at the bottom left of the menu To start up to open the settings window.
Step 4. Click Update & Security
This is the circular arrow icon in the settings window.
Step 5. Open the Windows Security tab
This tab is on the left of the window.
Step 6. Select Virus and Threat Protection
This option is in the middle of the window. Click on it to open the window Windows Defender.
You may need to pull down the Windows Defender window by clicking on the square at the top right before continuing
Step 7. Click Virus and Threat Protection Settings
This link is in the middle of the menu.
Step 8. Turn off the switch
under Real-time protection.
The header Real-time protection is at the top of the window.
Step 9. Choose Yes at the command prompt
This will reactivate Windows Defender.
Method 2 of 2: Uninstall a third-party antivirus program
Step 1. Find the other antivirus program on your computer
If you intentionally installed an antivirus program, you should know its name. Otherwise, it may be part of the installation process for another program that you recently installed. This means that you will need to look for a program whose name you don't even know.
Step 2. Open the Start menu
To open the menu To start up, click on the Windows logo at the bottom left of the screen.
Step 3. Select Settings
In the start menu, click on the star wheel icon to open the window Settings.
Step 4. Click Applications
This option is in the middle of the settings window.
Step 5. Sort by date if necessary
If you don't know the name of the antivirus program, you can narrow down your searches by showing recently installed programs and backing up from there. Click on the menu sort by then choose Installation date.
If you know the name of the antivirus program, skip this step
Step 6. Look for the antivirus program
Scroll through the list of installed applications until you find the program you need to uninstall.
If you haven't intentionally installed an antivirus program, you'll find the program you need to uninstall at the top of the list if your Windows Defender was only recently disabled
Step 7. Click on the name of the program
A button Uninstall will appear below the program name.
Step 8. Choose Uninstall
You will find this option under the program name.
Step 9. Select Uninstall at the command prompt
This will open the program uninstall window.
Step 10. Follow the on-screen instructions
Scroll through the instructions making sure to select the option Delete all files (or something like that) if asked if you want to keep residual files as well as applications.
Step 11. Remove other associated programs
Some anti-virus programs install additional programs to take care of things like online security. If you see other programs from the same developer or with a name similar to the program you just uninstalled, uninstall them as well before continuing.
Step 12. Restart your computer
Click on To start up
, select On Off
then choose To restart in the context menu. Your computer will restart as usual, after which the Windows Defender program should be reactivated and resume working.