PHP 公式，以防止来自 IP 的 http 请求数超过

我要防止黑客扫描我的网站页面，我发明了一个公式来控制时间跨度内的平均点击量，这是最好的解决方案吗？

function exceeded(){
  $limit=5;
  $span=15;
  $now=time();
  if($now-$_SESSION['lastDate']>=$span){
     $_SESSION['lastDate']=$now;
     $_SESSION['totalHits']=1;
     return false;
  }
  $_SESSION['totalHits']=($_SESSION['totalHits']*($span-($now-$_SESSION['lastDate'])))/$span;
  $_SESSION['totalHits']+=1; // Adds current Hit
  if($_SESSION['totalHits']<=$limit){
      $_SESSION['lastDate']=$now;
      return false;
   }
   $_SESSION['lastDate']=$now;
   return true;
}
//-----------------------------
if(exceeded()){
  echo 'You have exceeded your request limit come back in 15 seconds';
  exit;
}