Spam bot surname and mass delete

[PamelaE]

I have tried every solution available to get rid of stupid spam bots. I have stopped them posting but I don't want them even registering but ideally I would like to mass delete them.

I have noticed that 90% of them fill in the surname field with 12345 , is there not a solution to stop them registering if they type in numbers in this field?

Also, Im not sure if there is an option already, but if I do a search for users by surname, I get all the registered bots, like 100's but is there a way to mass delete rather than go in one at a time.

Thanks