Another suggestion. If CPhulk is not currently enabled, do enable it now and set it to notify you when there are 3 or more failed attempts. (You can set it to 1 or 2 if you wish).
I looked through records over the past 3 days and spotted hackers trying to login at some point. However the CPhulk email notification was in the frozen mails due to the tens of thousands of spam in queue.
If you do have these notifications setup, very likely the notifications were trigerred but stuck.