ISP Problem with Spam

I received the following from my ISP.

We have disabled the comment forms on your site.

It is not a matter of requiring logins to allow for posting comments, it is a matter that I see thousands (>12000 at one time) of emails sourced from your POST comment form.

This nice, shiny “comment post” form is what botnets look for to abuse
server resources regardless of the ability to actually post their spam, though if they are successful, which many are, then they spread their spam links to yet another unsuspecting blog host.

For any form on your website where there is a submit button, you should have some method of filtering out the non-human element on the internet. This would also include the wordpress login page as it is one of the more frequent targets.

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What is the solution using WordPress??