Thread:Project:Support desk/SPAM

MediaWiki 1.13.0 PHP 5.2.12 (cgi) MySQL 5.0.91-log

URL http://awqa.org/networkwiki/index.php?title=Main_Page

My wiki has been inundated by thousands of automated users that are editing and creating pages non-stop and overloading the system. I've restricted editing privileges only to registered users, but the 'bot is auto-generating users. How do I delete all of the existing illegitimate users and prevent future spam?