Comment spam, need help

Hey all,

I’ve been getting an insane amount of comment spam, and emails being sent out from my site (so says my network admin)

we’ve discovered there is a vulnerability in the file wp-comments-post.php and I’m not sure how to go about correcting this vulnerability, I’ve already tried deleting this and replacing with a fresh file.

Has anyone dealt with a wp-comments-post.php exploit like this before? Any tips on what I should do?

I read this article, looks promising, thoughts? comments?
https://davidwalsh.name/wordpress-comment-spam