Apple - How can I disable the Screen Saver on the login window?

I believe this does the trick (at least it seems to have worked for mefor several hours now):

sudo defaults write /Library/Preferences/com.apple.screensaver loginWindowIdleTime 0

This disables the screensaver in the loginwindow.

You can edit the .plist file at /Library/Preferences/com.apple.screensaver either using a text editor, Plist Editor (requires the OS X Developer Tools) or the defaults command in Terminal to remove the screensaver at login window.

Like this:

sudo defaults write /Library/Preferences/com.apple.screensaver loginWindowIdleTime 0

It isn't possible to disable the login screensaver in Mountain Lion due to a bug. According to https://discussions.apple.com/thread/4540671?start=0&tstart=0 the best you can do is log into root's screensaver settings and change it to Message which uses less resources.

See https://apple.stackexchange.com/a/16515/21181 for how to do that.