code: private void setFileNotWorldReadablePermissions(File file) {
         file.setReadable(false, false);
         file.setWritable(false, false);
         file.setExecutable(false, false);
         file.setReadable(true, true);
         file.setWritable(true, true);
      }
docs: This procedure sets permissions to the given file to not allow everybody to read it.
  
  Only when underlying OS allows the change.
  
  @param file File to set permissions