New user registrations – Spam?

Hey Folks –

I’m running 2.8.5, and about a month ago, I turned the “Membership: Allow anyone to register” feature on. I wanted to allow better comment threads by letting people register so I can see each other’s avatars in the comment stream, etc.

Since then, I’m getting daily “X people have registered” emails for people who are registering on my site. However, none of these emails actually are active in my comments section, and many of the email addresses look bot-created.

Can someone tell me:

1. What’s going on? Are these bots registering? For what purpose?
2. Any security issues I need to worry about here?