May hold off on changing over to something like Drupal or WordPress until this is sorted out. From Netcraft: PHP Blogging Apps Vulnerable to XML-RPC Exploits,
Many popular PHP-based blogging, wiki and content management programs can be exploited through a security hole in the way PHP programs handle XML commands. The flaw allows an attacker to compromise a web server, and is found in programs including PostNuke, WordPress, Drupal, Serendipity, phpAdsNew, phpWiki and phpMyFAQ, among others.