Add screening by IP address. When deleting a user as a spammer, block all signups from the same IP address.

lib/validators/allowed_ip_address_validator.rb

@@ -0,0 +1,9 @@
+class AllowedIpAddressValidator < ActiveModel::EachValidator
+
+  def validate_each(record, attribute, value)
+    if record.ip_address and ScreenedIpAddress.should_block?(record.ip_address)
+      record.errors.add(attribute, options[:message] || I18n.t('user.ip_address.blocked'))
+    end
+  end
+
+end