Microsoft acknowledged the growing threat of spyware with the launch of Windows Defender a few years back. It's available for all versions of Windows from XP onward. In Windows 8 and Windows 10, Microsoft provides an enhanced version of Defender that also protects against malware -- in essence rolling Security Essentials (Microsoft's free antivirus program) and Defender into one.
The revamped Windows Defender rubbed many security software companies up the wrong way, so Microsoft provided an option to turn off Defender when a trial version of a security suite was installed on a new PC or laptop. This is because the two may conflict with each other and cause performance problems.
However, if you don't activate that McAfee or Norton trial, Defender won't automatically enable itself, so you'll be vulnerable to malware. And that's not a good thing.
(If you don't like any of these options there are better free antivirus programs you can install -- see the best free antivirus software for more.)
How to check if Windows Defender is running
In Windows 10 Windows Defender has a small Shield icon that can be found in the taskbar, though in earlier versions of Windows you should look for a castle icon.
Look in the taskbar for this icon: it may be hidden in the more options menu, which you can access by clicking the upwards triangle icon.
If Defender is turned off and your PC is at risk you'll notice that the shield icon has a small cross on its bottom right corner. Click on this icon to launch the Defender app and find out for sure whether Defender is turned on or off.
If you can't find this icon, type Defender into the Start menu search bar or Start screen and select the top result, which should be Windows Defender. This will launch the app.
You'll notice that the screenshot shown here has lots of red on it - there's a red strip at the top, a big red Turn on button, and an image of a display with a red screen and a cross in it. This means Defender is turned off. Were Windows Defender turned on, all this red would be green.
If Defender is turned on but you still see a lot of red, this may be because Windows Defender requires you to update its definitions. You can allow it to search for updates from the main Windows Defender dashboard.
How to turn on Windows Defender
If Windows Defender is turned off, this may be because you have another antivirus app installed on your machine (check Control Panel, System and Security, Security and Maintenance to make sure).
You should turn off and uninstall this app before running Windows Defender to avoid any software clashes. You can uninstall apps in Control Panel, Programs, Programs and Features.
Launch Windows Defender using the methods outlined above, then hit the large red Turn on button. Defender will begin monitoring and protecting your computer
To find out exactly what Windows Defender is protecting, click the Settings cog icon on this screen. Confusingly, this will open the main Settings app on the PC
You should find that Windows Defender's Real-time protection is switched on, but you can also use this menu to toggle on and off cloud-based protection, automatic sample submission and enhanced notifications
How to turn off Windows Defender
To turn off Windows Defender, launch the app from the taskbar icon or by typing Defender into the Start menu search bar or Start menu. Now click the Settings cog icon and, in the window that opens, switch Real-time protection from on to off.
If you turn off Windows Defender in Windows 10 using the toggle buttons above, bear in mind that it's a temporary thing. Protection will be automatically re-enabled if necessary to keep your PC secure.