The username is one part of logon credentials that could be used to gain access to a system. Preventing the enumeration of users limits this information to authorized personnel.
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This applies to member servers. For domain controllers and standalone or nondomain-joined systems, this is NA.
If the following registry value does not exist or is not configured as specified, this is a finding.
Configure the policy value for Computer Configuration >> Administrative Templates >> System >> Logon >> "Enumerate local users on domain-joined computers" to "Disabled".