Who are the 'guests' that show up in my subscription only website?

I have a buddypress site with the Business Portfolio theme. I am using the WordPress Membersip plugin and only subscribers can see the protected content.

I also use the Visitor Maps and Who's Online plugin.

I am able to see any member who is online, but I also see 'guests'.

Who are these guests? I do not have any level set up for 'guests' and I certainly do no allow any 'guests' in the site without being registered subscribers, so who are they?

They are not bots as there is a place to see this and they are listed separately from guests.

Please let me know. It is imperative that I have full security on my site.