SB Search Exclude Category

sb-sec.php

<?php
/*
Plugin Name: SB Search Exclude Category
Plugin URI: https://svenbrier.de
Description: Für nicht angemeldete Benutzer eine Kategorie von der Anzeige in der Liste der Suchergebnisse ausschließen.
Version: 1.0
Author: Sven Brier
Author URI: https://svenbrier.de
License: GPLv2

Copyright 2016 Sven Brier (email : github@svenbrier.de)
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
add_filter( 'pre_get_posts', 'sb_sec_exclude_category' );

function sb_sec_exclude_category( $query ) {
    // If user is not logged in ...
    if ( !is_user_logged_in() ) {
        // ... and searching.
        if ( $query->is_search() ) {
            // Remove the matches from category with the ID 2.
            $query->set('cat', '-2');
            return $query;
        }
    }
}
?>