How to Turn on Windows Defender for Windows 10

To start Windows Defender, you have to open the Control panel and Windows Defender Settings and click on Turn On, and ensure that the following are enabled and set to On position:

1. Real-time protection
2. Cloud-based protection.

When there is no security software protecting your computer, you will see notifications like these appear.

Check virus protection notification

Clicking on it will show you the installed security apps on your system. If you miss this notification, you can see it in the Notification & Action Center.

Security and Maintenance menu

Clicking on it too will show you the installed security apps on your computer, as follows.

Security and Maintenance windows listing security applications currently installed

Select Windows Defender and then click on the Turn on button. Windows Defender will start. The first think you want to do when this happens, is to update your definitions.

Windows Defender window with Update tab open

Clicking on the Settings link in the top right corner will open the following panel. You can also access it via Settings > Update & security > Windows Defender.

Update & Security setting toggles

Once here, ensure that Real-time protection and Cloud-based protection is set to On. You may also set Automatic sample submission to the On position. You may then configure Windows Defender according to your needs.