I have get this problem. one day registering to 200 members . But resolves using this stapes

1 step
Protector »» Preferences
Band the ip no limit

2 step
modules/profile/admin/field.php
go to profile and creating some Felds are require states
E.g.:- name , location etc.

Add to basic field to something word you like “ I’m not robot ” and its require

Not_Robot_ please Add this Word " im not Robot " Text Field Toggle Required

Test
http://freewebdevelopers.tk/modules/profile/register.php

this step using i can stop all spamming