Windows Defender in Windows 8.1 and Microsoft Security Essentials in Windows 7 and Windows Vista help protect your PC from malware and other threats in exactly the same way. You can't use Microsoft Security Essentials with Windows 8.1.
Windows Defender in Windows 8.1 is built into Windows and ready to work as soon as you turn your PC on.
Microsoft Security Essentials works on Windows 7 and Windows Vista. You can download it from the Microsoft Security Essentials website.
Before the release of Windows 8.1, Windows Defender was a separate tool for antispyware. This tool is no longer supported, as it is now fully integrated into Microsoft Security Essentials (in Windows 7 and Windows Vista) and Windows Defender (in Windows 8.1).
In other words, you don't need to have both Microsoft Security Essentials and Windows Defender if you're using Windows 7 and Windows Vista.
You can find out more about using our products on our security software help page.
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