Bryan Carl Morales

For this, you need to edit the file ‘meta-boxes.php’ located in wp-admin/includes/ folder.

Open that file in NotePad and find the following code:

$visibility = ‘public’;

$visibility_trans = __(‘Public’);

Now, all you need to do is change it do the following:

$visibility = ‘private’;

$visibility_trans = __(‘Private’);

Done.

via WordPress › Support » How to set new posts visibility to private by default ?.