John is a keen administrator, and has followed all of the best practices as he could find on securing his Windows Server. He has renamed the Administrator account to a new name that he is sure cannot be easily guessed. However, there are people who already attempt to compromise his newly renamed administrator account.

How is it possible for a remote attacker to decipher the name of the administrator account if it has been renamed?

A.
The attacker used the user2sid program.

B.
The attacker used the sid2user program.

C.
The attacker used nmap with the -V switch.

D.
The attacker guessed the new name.

Explanation:
User2sid.exe can retrieve a SID from the SAM (Security Accounts Manager) from the local or a remote machine Sid2user.exe can then be used to retrieve the names of all the user accounts and more. These utilities do not exploit a bug but call the functions LookupAccountName and LookupAccountSid respectively. What is more these can be called against a remote machine without providing logon credentials save those needed for a null session connection.