This is a security hole in my opinion and should be plugged by editing the lock screen ui layout:
vi /usr/share/mate-screensaver/lock-dialog-default.ui
#find these objects and set the visible property to false
object class="GtkLabel" id="note-tab-label"
object class="GtkLabel" id="auth-username-label>
object class="GtkLabel" id="auth-realname-label"........