Interesting fact: There’s no need to install Microsoft Security Essential on Windows 8:
According to Microsoft…
In Windows 8.1 and Windows RT 8.1, Windows Defender provides the same level of protection against malware as Microsoft Security Essentials. You can’t use Microsoft Security Essentials with Windows 8 and Windows RT, but you don’t need to—Windows Defender is already included and ready to go.
Sigh. Which means if you want to install it as a backup to catch what McAfee and Norton never can, it’s not going to be easy. Good luck to those that try. Read the related articles and links to fully understand