For those who haven't yet discovered it: the latest security update has broken Network Preferences for most users. The preference pane will repeatedly pop up a warning that reads, "Network preferences have been changed by another application." Then the only way to exit system preferences is to force quit it.
There's a workaround, thanks to tonza on the Apple forums. Just go to Security preferences and check "Require password to unlock each secure system preference".
There's a workaround, thanks to tonza on the Apple forums. Just go to Security preferences and check "Require password to unlock each secure system preference".