How to hide a user from the gdm login screen?

Hi

I'm using openSUSE 13.1 with gnome3 gdm

I want to hide a certain user from the list of available logins.

I have edited the /etc/gdm/custom.conf and put this is there:

... but this changes nothing. The user is still visible.

I also tried to give the user a ID lower than 1000 but this also does not work.

Any suggestion want I should do to acomplish this?