Invoked by the Javascript tracker when the control code (nonce) sent by the browser is not valid for the payload associated to it.

// Make sure that the control code is valid
list(self::$data_js['id'], $nonce) = explode('.', self::$data_js['id']);
if ($nonce !== md5(self::$data_js['id'].self::$options['secret'])){
	do_action('slimstat_track_exit_103');
	self::$stat[ 'id' ] = -103;
	self::_set_error_array( __( 'Invalid data signature. Try clearing your WordPress cache.', 'wp-slimstat' ) );
	self::slimstat_save_options();
	exit('-103.0');
}