Lately we have seen a huge increase in attacks against xmlrpc.php in wordpress-installations. This creates problems for other clients on the hosting servers, and for yourself.
To protect yourself against this you can use the following guide:
http://docs.host1.no/wiki/Securing_your_Wordpress_installation (See «bruteforce against xmlrpc.php».)
Add a .htaccess-file to the directory with wordpress (and xmlrpc.php) in it, copy the lines mentioned in the wiki-article into the .htaccess-file and your xmlrpc.php should be protected against any attacks.