Hey there @edwardiangaiety,
Membership 2 adds a separate registration process to your site, as I’m sure you noticed. So it’s possible what happened here is that you didn’t add any CAPTCHA or anything to protect from spam sign ups on that page. That could have been how they initially got in.
We include support for:
WP reCAPTCHA: https://en-ca.www.ads-software.com/plugins/wp-recaptcha/
Are You a Human: https://en-ca.www.ads-software.com/plugins/are-you-a-human/
So if you ever decide to give Membership 2 another shot then I would recommend using one of those 2 spam sign up blockers as well. With any plugin that involves registration forms you will be susceptible to spammy sign ups. We’ve included ways to help counteract that, but of course it’s up to the user whether they want to take advantage of them or not.
I do realize it’s unlikely you will decide to use this plugin again, but just wanted to mention the above CAPTCHA options in-case you do.
If you are still receiving sign ups even with Membership 2 deactivated then you must have a security hole somewhere else as well. I would make sure you don’t have any spam admin accounts or any accounts that have permissions to create users.
You can try temporarily locking up your registration via: WordPress > Settings > General.
Then see if you are still receiving sign ups. If so, it’s coming from inside your site, so make sure you clear out all of the spam users and also do a security scan on your site for any compromised files or ask your host too.
Hope that helps!
Cheers,
Tyler