Reference: Configure Services Dialog
This field is available only on NT platforms, and then only when configuring THIS COMPUTER. It enables NT security checking in place of the Beyond FTP security system. All user names and passwords are checked against NT accounts, and access to shares is controlled by the NT operating system. Beyond FTP MUST be run under the Local System Account for this to work properly. See the tutorial subject Changing Beyond FTP Startup Security for instructions on making this change. All valid NT users are assumed to possess the Key Retrieval attribute.