Joaquim, if the context in which you are deploying DokuWiki requires additional information hiding, you should tweak the template not to display any footer (page name, lastchange and user who did the change), breadcrumbs, backlinks and certainly restrict access of some actions to registered users. Going further, some actions can (should in your case) be disabled. Feeds are also leaking some information. The default template (and default behaviour) of DokuWiki is probably not ideal for some special setups or contexts, but it can be tweaked to fit better.
Note that this patch was applied last week:
user: Andreas Gohr <email@example.com
date: Fri May 11 19:21:16 2007 +0000
summary: hide namespaces from index when no read permissions are available FS#427
eb, feel free to submit your patches to the mailing list.