Kimon Andreou wrote:
Like Schnee said, you'll have to mess with the database It's easy if the user has not made any edits. If they have, then it get very tricky and you have to know what you're doing. And that's beyond the ethical/legal aspects that Schnee brought up.
You may want to consider using the RenameUser extension to rename the user to something unusable such as "DELETEDUSER_{username}", add the user to a new user group and prevent that user group from editing, viewing, etc. effectively disabling the account and releasing the username for use by a new user.
Kimon
You can't prevent a group from doing things. Permissions are additive, so you *allow* them to do things. There's an extension on mediawiki to delete users by merging them with a deleted_users account.