Active Users (A PHP Script)

A member of a forum I frequent needed an active users online script so I wrote up the below for him.  It’s an overdone and unoriginal script but maybe someone will find it useful.

<?php
 
$CONFIG = array ();
$CONFIG["visitor_file"] = "visitors.txt";
$CONFIG["timeout"] = 60;
 
if (file_exists ($CONFIG["visitor_file"]))
{
  $curData = unserialize (file_get_contents ($CONFIG["visitor_file"]));
  $curTime = time ();
 
  $newData = array ();
  $userInFile = false;
 
  if (count ($curData) > 0)
  {
    foreach ($curData as $ip => $timeOfLastVisit)
    {
      if ($curTime - $timeOfLastVisit >= $CONFIG["timeout"])
      {
        continue;
      }
 
      if ($ip == $_SERVER["REMOTE_ADDR"])
      {
        $userInFile = true;
        $newData[$ip] = time ();
      }
      else
      {
        $newData[$ip] = $timeOfLastVisit;
      }
    }
  }
}
 
if (!isset ($newData) || count ($newData) == 0 || (isset ($userInFile) && !$userInFile))
{
  $newData[$_SERVER["REMOTE_ADDR"]] = time ();
}
 
file_put_contents ($CONFIG["visitor_file"], serialize ($newData));
 
echo count ($newData);
 
?>