This setting controls whether the Net Logon service will allow the use of older cryptography algorithms that are used in Windows NT 4.0. The cryptography algorithms used in Windows NT 4.0 and earlier are not as secure as newer algorithms used in Windows 2000, Windows XP, Windows Server 2003, Windows Vista, and this version of Windows.
By default, Net Logon will not allow the older cryptography algorithms to be used and will not include them in the negotiation of cryptography algorithms. Therefore, computers running Windows NT 4.0 will not be able to establish a connection to this domain controller.
If this setting is enabled, Net Logon will allow the negotiation and use of older cryptography algorithms compatible with Windows NT 4.0. However, using the older algorithms represents a potential security risk.