Maybe it really worths to close registration for that period?
It worths but we already have many spammer accounts created.
OK, I'm block account creation for now.
Once improved the captcha, would it be possible to reset the user list and remove all users that has not made any edit in its life? Because, why do a user need one wiki account if it doesn't edit the wiki?
I guess so. That needs to be investigated too.
During the last user merge and deletion sessions I've noticed that the user posted more files than the shown in the Recent Changes list. For example, I notice that one user registered, then created a spam page and uploaded an image file. When the account is merged and deleted and the database restored, there appear more modified pages and images uploaded to be removed... Maybe the wiki is reading its IP?
I'm not sure - partially that may be a bugs in UserMerge, partially - the way how wiki deals with renamed pages...