I am not able to find a particular user name which is used to login over ssh, in /etc/passwd and /etc/shadow file. Login attempt is successful because I can found that username when I issue "w" command (“w” command is same as “who”).

Strange thing is that I can even create user with same name with which I am already logged in (no error reported). I think user creation is also successful because, now I can find the user name in /etc/passwd file. But when I try to delete that user an error occur (telling that user already logged in).

Any idea about this issue??????? Mind that I am using SSH to connect Linux. I think my Linux is bit different.
Here is the description about the OS... OS name - Linux, OS release - 2.6.14VENTURI64, OS version - #5 SMP.
Any idea how to configure a user like that??????????????

Thanks
Subrata