Totally disables XMLRPC, preventing the recent Pingback spam vulnerability.
There's a vulnerability in WordPress's XMLRPC implementation, that permits trackback spam - even when you disable trackbacks.
The only way to prevent this spam is to disable XMLRPC entirely. Some people have suggested renaming or deleting the xmlrpc.php file, but this is not a good idea, because it's altering core code and not trivial for novice users to undo.
This plugin completely disables WordPress's XMLRPC functions, and doesn't alter or rename any core files. You can enable XMLRPC again by simply disabling this plugin.
See http://www.acunetix.com/blog/web-security-zone/wordpress-pingback-vulnerability/ for detailed information about the vulnerability in WordPress's XMLRPC handler.