Wordpress releases urgent security fix for hole in XML-RPC implementation
A security issue has been located that enables a specifically crafted request to allow a valid user to edit any post on the blog.
Wordpress has released a fix.
The recommended action is to update Wordpress to 2.3.3 (which includes a couple of other minor tweaks) or for those seeking a quicker, easier to implement solution to fix the security flaw only, download an updated xmlrpc.php file from Wordpress and over-write your existing xmlrpc.php file in your Wordpress root folder.