To be protected against this cyber attack, do not forget to restrict access to /xmlrpc.php resource only from your IP address (1.2.3.4 in the example below).

For Apache, edit /.htaccess file to add:

<Files "xmlrpc.php"> 
   order deny,allow 
   deny from all 
   allow from 1.2.3.4 
</Files>

Save the changes, restart apache and ready!