UNIX offers a service called ident or auth which will identify the user of a TCP connection. In the intended operation of this feature, when a user connects to a server, the server sends back a request to the ident service to discover the user's identity.
However, it can also be used in a reverse way. If a server itself also has the ident feature turned on, when a user connects the the server, the user can query the identify of the service it is connecting to.
This helps discover possible accounts that can be broken into.
