[Defender Pro] Defender Event Log

This is an interesting discovery that I just made when I got an email from the Defender plugin saying that I had 171 Events Logged. The events say that they are failed login attempts using the two usernames that we have added to the site.

I have had no failed login lockouts. The message shows my username, NOT my ip address and as a matter of fact…all of the events seem to be the same thing but from different ip addresses.

Question is…how does someone know my usernames in the website? This is a fairly new site and we have the search engine off. Do I need to be concerned about this activity?