New subscriber or hacker??

Hello,

This is such a newb question I’m almost embarrassed to ask it.

I’ve recently set up a wordpress blog and I just got an email saying “New User Registration” and it has details of some person I don’t know who seems to have signed up to my blog. In the wp-admin their user role is shown as ‘none’ but I don’t understand how they did this. Does this mean they are just subscribed to my RSS feed or something, or have they exploited a weakness in my site and somehow gained access to parts of the site they shouldn’t have?

Bit worried. Any advice would be helpful! I’m a little unsure of how it all works

Thanks