protected function checkFile($fileName, $checkSum)
 {
     if (time() - $this->startTime > 24) {
         $_SESSION['corruptedFiles'] = $this->corruptedFiles;
         $this->echoMessage($this->getCheckingMessage(), $this->getRedirectUrl($this->filesCheckedSoFar));
         exit;
     }
     $this->filesCheckedSoFar++;
     if ($this->filesCheckedSoFar <= $this->progress) {
         return;
     }
     $file = new Gpf_Io_File('../' . $fileName);
     try {
         if ($file->getCheckSum() != $checkSum) {
             $this->corruptedFiles[ltrim($file->getFileName(), '\\.\\.\\/')] = $this->_('CORRUPTED');
         }
     } catch (Gpf_Exception $e) {
         $this->corruptedFiles[ltrim($file->getFileName(), '\\.\\.\\/')] = $this->_('MISSING');
     }
 }