http://sn.1w6.org/file/pztrn-20140815T115726-flgy7s3.html
If spammer spams manually, not using bot - there is no safe place at all. But with #QuestionCaptcha and #EmailRegistration and #MailBlacklist plugins I cut 100% of bots, there was no automatic registrations for last 6 months at all. Second plugin is bundled with #gnusocial, other 2 can be found at http://url.pztrn.name/1lp