MS Baseline Security Audit Failure

I really need some advice.

While running MS Baseline Security Analyzer, I noted the
following:

1) detection of more two Admin Accounts, as follows:

A) Administrator
B) Angela
C) S-1-5-21-4758197-677485609-1728312259-1003

Questions - What is the third account ("C") and how can I
delete it? Note that I did not knowingly set this
account up.

2) When I reviewed the event logs for the time period
during the run of MS Baseline Security Analyzer I noticed
hundreds of Failure Audits with ID Code of 627 and the
following description:

SE_AUDITID_USER_PWD_CHANGED

The Target Acount ID varies with each logged failure but
follows this format:

OURDOMAIN\SUPPORT_388945a0
OURDOMAIN\SUPPORT_b326ad0c
OURDOMAIN\HelpAssistant
OURDOMAIN\Administrator
OURDOMAIN\Angela

Question - Microsoft's support site suggests "This event
might indicate that someone is trying to get the password
of another user."

Is this related to a misconfiguration of Windows settings
in combination with using MS Baseline Security Analyzer
OR is somebody trying hack into my computer?

Any insight or help with this mystery would be greatly
appreciated.