Login Activity list question

I noticed that my when I download my Admin activity I see all the different admin login details and activity...but I also see an admin ID 0 which I dont know who that is or whether that a ligitimate admin login...I have 5 admins who have diffent password and access rights. I am the Only admin (superuser). but I also see a admin ID that says 0, who or what could this mean.

0 means the visitor was not logged in yet. The next entry should be the login screen, and then once logged in a number will be assigned.

If you see 0 repeatedly on pages that should not be allowed access without login, then you should fix whatever problems are allowing such unauthorized access.