can i track Ip by username upon logon

[davy19]

YaBB SE Version: 1.5.5
Server Platform: Unix, Linux, or BSD

Problem Description:
anyway to track to see if a person is sharing a username with multiple people?

I know if you make a post it stamps it with the IP, but i am not worried if they post just worried if people should no be seeing something they should not be becuase they dont have access.

Basically jsut want to know everytime someone logs into the forums where they are logging in from and if bieng used at same time from two different machines?

Thanks