Device host name in terminal shown as DEVICE_MAC\...

[sand49]

Hi when i open my terminal it says my host name is my mac address, the prompt looks like this:

User@DEVICE_MAC\0000\00000\00000\00000\00000\00000\000 ~ $

I have replaced my real user name and mac address for security.
My host name also shows up like this at the top of firefox and other Xorg based web applications that show the host name at the top of the window.
Btw I'm using networkmanager nm applet in xfce.

Thanks for the help .

[Roman_Gruber]