def start_async_check_update(self, now=False, callback=None):
		"""Start a background thread which will check for updates"""
		if self._async_checking:
			return
		self.print_verbose("Starting background checking thread")
		check_thread = threading.Thread(target=self.async_check_update,
										args=(now, callback,))
		check_thread.daemon = True
		self._check_thread = check_thread
		check_thread.start()