I actually have a rather different security problem. I would like to set up a non-firewalled wiki but only a certain group should have access. This may be for legal reasons, but has been imposed as a requirment that I cannot get around. Anyone know of a wiki that restricts access in such a way?

Why not use webserver passwords to restrict access? Or do you wish to restrict editing by a restricted group? -- AnonymousCoward ;)

Even restricting the editing could be done easily using the security the webserver provides.

OTOH, few users have ".htaccess" enabled for them, and even fewer have access to the "httpd.conf".