For some stupid reason microsoft decided to remove the icon for Windows Defender in the system tray for windows 8. This article shows you how you can restore this functionality. It does require the installtion of an free app.

"I noticed one glitch, which seems to place a red “X” over the icon indicating Defender is disabled, even though it is not."

I found a solution to this "bug" from a user at neowin.net: "The program checks the registry for a certain key, however this key is not created by default. You have to disable Windows Defender (under the settings tab, uncheck 'use real-time protection...' save changes, then recheck it and save changes). This creates the registry value and sets it to '1'."

That did the trick for me and the X becomes a check. :)