ddos атака зачем и как защититься от нее

 <?php
function agent() {
$arr=file('useragent.txt');
$agent =$arr[rand(0,count ($arr)-1)];
return $agent;
}
function proxy() {
$arr2=file('proxy.txt');
$proxy =$arr2[rand(0,count ($arr2)-1)];
return $proxy;
}
$header [] = "Accept: text/html;q=0.9, text/plain;q=0.8, image/png, */*;q=0.5";
$header [] = "Accept_charset: windows-1251, utf-8, utf-16;q=0.6, *;q=0.1";
$header [] = "Accept_encoding: identity";
$header [] = "Accept_language:  ru-ru,ru;q=0.5";
$header [] = "Connection: close";
$header [] = "Cache-Control: no-store, no-cache, must-revalidate";
$header [] = "Keep_alive: 300";
$header [] = "Expires: Thu, 01 Jan 1970 00:00:01 GMT";
$agent = agent();
$proxy = proxy();
$cook = 'cook.txt';

$ch = curl_init($data);
curl_setopt($ch,CURLOPT_RETURNTRANSFER,1);
if(!empty($_POST['proxy'])) {
curl_setopt($ch,CURLOPT_PROXY,$proxy);
}
     @curl_setopt ( $ch , CURLOPT_VERBOSE , 1 );
     @curl_setopt ( $ch , CURLOPT_HEADER , 1 );
     @curl_setopt ( $ch , CURLOPT_USERAGENT , $agent );
     @curl_setopt ( $ch , CURLOPT_REFERER , $path );
     @curl_setopt ( $ch , CURLOPT_HTTPHEADER , $header );
curl_setopt($ch,
CURLOPT_COOKIEJAR,
$cook);
curl_setopt($ch,
CURLOPT_COOKIEFILE, $cook);
curl_setopt($ch,CURLOPT_POST,0);
curl_setopt($ch,CURLOPT_POSTFIELDS,$post);

     @curl_setopt ( $ch , CURLOPT_FOLLOWLOCATION , 1 );
     @curl_setopt ( $ch , CURLOPT_SSL_VERIFYPEER, 0 );
     @curl_setopt ( $ch , CURLOPT_SSL_VERIFYHOST, 0 );
$page = curl_exec($ch);
if(preg_match($seek,$page)) {
print $page;
}