Yesterday we had [this][1] specific example of the user where he/she came into the site, posted five (or so) questions some of them plagiarised and deleted, some of them marked as duplicate, and others closed for other reasons, even the only question leftover is actually plagiarised, marked not so only for technical reasons. 

This attracts bad content and sets bad precedence, how do we handle such users, if we dont do anything about it, it wont be long before we would just be copies of cheap riddle sites.

Can we not plain delete such users, not sure if SE has a policy on unregistered users.