This check determines whether the built-in Guest account is enabled on the scanned computer.
The Guest account is a built-in account used to log on to a computer running Windows XP, Windows 2000, or Windows NT when a user does not have an account on the computer or domain, or in any of the domains trusted by the computer's domain. Windows XP computers map incoming user connections from across a network to the local Guest account when simple file sharing is enabled. If the Guest account is enabled on Windows NT, Windows 2000, and Windows XP machines (not using simple file sharing), it will be flagged in the security report as a vulnerability. If the Guest account is enabled on Windows XP machines that use simple file sharing, it will not be flagged as a vulnerability.
What's New in Security for Windows XP Professional and Windows XP Home Edition (details use of the Guest account in the Windows XP simple sharing model)
Users overview (Microsoft Windows 2000 Advanced Server Documentation)
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