Code:
<?

$filename="counter.txt";
if(!(@chmod($filename,0600)))
    report("Cannot write to file - $filename");

$counts=intval(loadfile($filename));
$counts++;
if(savefile($filename,$counts))
    report("$counts");
else
    report("Cannot write to file - $filename");


function savefile($fname,$data) {
     if(!file_exists($fname))
          report("File nout found - $fname");
     $f=fopen($fname,"w");
     fwrite($f,$data);
     fclose($f);
     return true;
}
function loadfile($fname) {
     if(!file_exists($fname))
          report("File nout found - $fname");
     $f=fopen($fname,"r");
     $data=fread($f,filesize($fname));
     fclose($f);
     return $data;
}

function report($msg) {
     die("&counter=$msg&");
}

?>