I'm getting comments when I didn't check "Allow comments"

All of a sudden, I’m getting a lot of spam-like comments to approve even though I had not checked “Allow Comments” on any of my pages (thankfully, they are not showing up on my pages, but they are being emailed to me to approve). My Discussion settings weren’t very restrictive, but I didn’t think they had to be if I wasn’t allowing comments anyway. I also don’t quite understand how anyone was able to post comments when there wasn’t anything to click for them to do that.
I’ve tightened up my discussion settings, but I still wonder what this is, how it’s being done, and how to be sure to stop it.
Has anyone else had a similar problem? Is this some kind of hacker attack?
Thanks.