Aaron Schulz wrote:

http://www.mediawiki.org/wiki/Extension:CheckUser might be useful too.

Either way, you need to upgrade mediawiki to use any of those extensions.

Thanks! I've actually hacked this enough that upgrading will be quite painful, so I ended up putting up a captcha for edits. Maybe later I'll add an option to suppress the captcha for validated users.

Thanks again, Aerik