Nope, Windows defender gets its virus signatures via Windows Update.
If you read this Microsoft documentation you will see they make mention to updates taking place via WSUS (this is just a corporate front end for Windows Updates).
MSE was a separate product and not part of Windows, whereas Defender was included in Win7 by default.
MSE's features have now been rolled into Defender, and so a separate install isn't required any more on Win8.@Karan My bad.
You can also have Windows Defender check online for updated definitions before scanning.
According to that, you can also have Defender do an (extra) check for definitions before starting a scan but.
There is no UI control for that available, but you can easily modify how the scheduled scan is launched and with what options Windows Defender is working.
I don't like automatic updates as I don't want to install useless updates like the ballot screen or something else, I want to choose.From the Windows 8 Help and Support regarding Defender: To help keep your definitions up to date, Windows Defender works with Windows Update to automatically install new definitions as they're released.AFAIK MSE cannot be installed in Win8 to replace Defender, as was possible in Win7.If you know of a hack or get it to work reliably/stably, it would be nice if you can share in a separate thread.It looks like the Windows Defender in Windows 8 won't upgrade the signatures automatically, if Windows Update is set to "Notify, but don't install the upgrades".
Since Defender updates are delivered with Windows Updates, then just like other Windows Updates, if you have it set to Notify Only, it will wait until you OK it.