Just go to comments tab in Dashboard and locate “Screen options” in upper right
My problem was that I had another blog which was not used very actively and had collected
over 2000 spam messages. In Eordpress you are able to delete many spam
messages at once by using the bulk action.
Usually the “Show on screen” is able to show you just few messages on Comments page
by default but you are able to put 100 in “Comments” amount
slot. This really speeds up if you are a victim of spam bot attack.
I deleted over 2000 spam messages with this technique in just five minutes.
Do not be stupid
However I recommend you to use some spam fighting plugins or another more intelligent ways that will
fight bots and they are unable to register at all. There are plugins that asks questions and you are
also able to decide what questions will be asked. Bots are not very clever answering questions because
them are just programmed to register and login and post a spam comment. Bots are not usually
designed to answer specific questions in some specific topic. This fact makes the bots stupid.