WordPress has an option that allows anyone to go to WordPress’s registration page and create a WP user account. This WordPress feature can open your site up for spam user registration.
If you are getting a lot of spam WP user registration and you are not sure where it is coming from then this option is likely the cause for it.
You can find this settings option in the General WordPress settings menu of your site.
Settings -> General -> Membership
Our Simple Membership plugin DOES NOT need that option to be enabled.
So you should keep the “Anyone can register” checkbox unchecked.
All membership registration should go via Simple Membership plugin’s registration form.