It's user's default login prompt. Perhaps you've (or user) changed some shell initialization file (.bashrc or .profile etc) where earlier prompt was set. Well, you can set it again as:
Add following line at the end of user's .bashrc or .profile file:
export PS1="[\u\@\H\]# "
export PS1="[$(whoami)\@$(hostname)]\# "
And then source the file:
~$ source .bashrc
~$ source .profile