How are others blogging on my site?

I am getting notices that a blog has been submitted to my site. It is obvious spam, but what I don't understand is how this is happening. I don't think I have any settings that allow anyone else to blog and that all posts and comments need to be approved by me. Can you check my settings and see if I have missed something? I have had the blog (although not active) up for a while but this is a recent occurrence.

All the users except you and me are unknown to me and are probably spammers.