BOT users getting to my site

I currently use the WP Membership plugin to control access to the website and it has been working fine. All members, I thought, were listed under that plugin. However, I found 35,000 plus users listed under the standard WP users list. All of them were users with blogspot in their nickname or someone from a .ru domain. I have a captcha set up for my registration page on WP membership. How can I block these people? I’m deleting 100 users per day now.

The page I need help with: [log in to see the link]