In UNIX/Linux the information about users is kept in the /etc/passwd file. Each line represents a user. The fields in each line are as follows: username, password,UID,GID,Gecos,home directory,shell Today the paswords are usually kept separately hence in this file you will only see an x in the second field.

When someone breaks in to a UNIX/Linux machine she might try to setup a user with UID 0 in order to gain root (superuser) access to the machine. Please check the following file and print a message if there is a user with 0 as UID which is NOT the root user.

examples/shell/etc_passwd.txt
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
cracker:x:0:99:games:/usr/games:/bin/sh
games:x:5:60:games:/usr/games:/bin/sh