spam_domain_prevention()

        public function spam_domain_prevention(){
            $this->timer('Spam Domain Prevention');

            //Skip lookups if user has already been checked or for logged in users.
            if ( (isset($this->super->cookie['spam_domain']) && $this->super->cookie['spam_domain'] === false) || is_user_logged_in() ){
                return false;
            }

            if ( $this->get_option('spam_domain_prevention') ){
                $spam_domain_array = $this->get_spam_domain_list();
                $ip_address = $this->get_ip_address();

                if ( count($spam_domain_array) > 1 ){
                    //Check the Referrer
                    if ( isset($this->super->server['HTTP_REFERER']) && $this->contains(strtolower($this->super->server['HTTP_REFERER']), $spam_domain_array) ){
                        $this->ga_send_exception('(Security) Spam domain prevented. Referrer: ' . $this->super->server['HTTP_REFERER'], true, array('security_note' => 'Spam Referrer'));
                        do_action('nebula_spambot_prevention');
                        header('HTTP/1.1 403 Forbidden');
                        wp_die(
                            'Access forbidden.', //Message
                            '403 Forbidden', //Title
                            array(
                                'response' => 403, //HTTP status code
                                'back_link' => false //Remove the back link
                            )
                        );
                    }

                    //Check the Remote Host (the hostname of the client making the request)
                    if ( isset($this->super->server['REMOTE_HOST']) && $this->contains(strtolower($this->super->server['REMOTE_HOST']), $spam_domain_array) ){
                        $this->ga_send_exception('(Security) Spam domain prevented. Hostname: ' . $this->super->server['REMOTE_HOST'], true, array('security_note' => 'Spam Hostname'));
                        do_action('nebula_spambot_prevention');
                        header('HTTP/1.1 403 Forbidden');
                        wp_die(
                            'Access forbidden.', //Message
                            '403 Forbidden', //Title
                            array(
                                'response' => 403, //HTTP status code
                                'back_link' => false //Remove the back link
                            )
                        );
                    }

                    //Check the Server Name (the server's domain name)
                    if ( isset($this->super->server['SERVER_NAME']) && $this->contains(strtolower($this->super->server['SERVER_NAME']), $spam_domain_array) ){
                        $this->ga_send_exception('(Security) Spam domain prevented. Server Name: ' . $this->super->server['SERVER_NAME'], true, array('security_note' => 'Spam Server Name'));
                        do_action('nebula_spambot_prevention');
                        header('HTTP/1.1 403 Forbidden');
                        wp_die(
                            'Access forbidden.', //Message
                            '403 Forbidden', //Title
                            array(
                                'response' => 403, //HTTP status code
                                'back_link' => false //Remove the back link
                            )
                        );
                    }

                    //Check the Network Hostname (reverse DNS lookup of the client IP address)
                    if ( isset($ip_address) && $this->contains(strtolower(gethostbyaddr($ip_address)), $spam_domain_array) ){
                        $this->ga_send_exception('(Security) Spam domain prevented. Network Hostname: ' . $ip_address, true, array('security_note' => 'Spam Network Hostname'));
                        do_action('nebula_spambot_prevention');
                        header('HTTP/1.1 403 Forbidden');
                        wp_die(
                            'Access forbidden.', //Message
                            '403 Forbidden', //Title
                            array(
                                'response' => 403, //HTTP status code
                                'back_link' => false //Remove the back link
                            )
                        );
                    }

                    //Check Query String of the requested page URL. Note: Commented out as we are now checking the entire URI below
                    // if ( isset($_SERVER['QUERY_STRING']) && $this->contains(strtolower($_SERVER['QUERY_STRING']), $spam_domain_array) ){
                    //     $this->ga_send_exception('(Security) Spam domain prevented. Query String: ' . $_SERVER['QUERY_STRING'], true, array('security_note' => 'Spam Query'));
                    //     do_action('nebula_spambot_prevention');
                    //     header('HTTP/1.1 403 Forbidden');
                    //     wp_die(
                    //         'Access forbidden.', //Message
                    //         '403 Forbidden', //Title
                    //         array(
                    //             'response' => 403, //HTTP status code
                    //             'back_link' => false //Remove the back link
                    //         )
                    //     );
                    // }

                    //Check the entire URL of this requested page (including the query string)
                    if ( isset($_SERVER['REQUEST_URI']) && $this->contains(strtolower($_SERVER['REQUEST_URI']), $spam_domain_array) ){
                        $this->ga_send_exception('(Security) Spam domain prevented. URL: ' . $_SERVER['REQUEST_URI'], true, array('security_note' => 'Spam domain in the requested URL'));
                        do_action('nebula_spambot_prevention');
                        header('HTTP/1.1 403 Forbidden');
                        wp_die(
                            'Access forbidden.', //Message
                            '403 Forbidden', //Title
                            array(
                                'response' => 403, //HTTP status code
                                'back_link' => false //Remove the back link
                            )
                        );
                    }
                } else {
                    $this->ga_send_exception('(Security) spammers.txt has no entries!', false);
                }

                $this->set_cookie('spam_domain', false);
            }

            do_action('qm/info', 'Spam Domain Check Performed');
            $this->timer('Spam Domain Prevention', 'end');
        }