The Finger protocol (RFC:1288) specifies a way of quering a server to ask information about who is logged in, and information about users, such as their realname, the last time they logged in, the contents of their .plan file (which is supposed to contain information on projects they are currently working on) etc.

Usually disabled now as it's considered a security risk and a information leak.

the Moris worm exploited a buffer overflow in the FingerServer to propergate.