Disable Comments (Due To Spam)

Can anyone tell me which PHP file I need to get rid of in order to stop the comment spamming?

I have WP configured to not accept comments on posts, and also require a visitor to be registered before posting comments. And yet, spam comments are getting through via spambots. They must recognize the file structure or something, since I stripped all references to commenting out of my template files. (The site is used for news postings, and I have a separate forum if visitors want to comment.) Obviously it’s a flaw in WP that if you “disable” commenting, the spambots are still able to access the commenting script and leave comments. They’re harmless, as they sit in the moderation queue, but they should NOT be showing up at all…in any forum software I’ve used, if you turn off posting privileges, nobody (not even spambots) can post.

I’m not going to install any anti-spam plugins: I just want to disable commenting completely. If WP worked correctly, spambots would not be able to circumvent this. Which file do I rename or delete to stop the spambots? I just want commenting completely gone.

TIA.