By now you know that you can log in as the user virtualbsd and its password is virtualbsd. Maybe you even changed the password and would like to change that message to something else, right? Here's how:
1) Open a terminal (right click anywhere on the desktop and select Terminal from the menu).
2) Type the following command (cust & paste is your friend if you are lazy):
su -m root -c 'mousepad /usr/local/lib/X11/xdm/Xresources > /dev/null 2>&1'
3) Type root's password (root4u) when prompted for it to start the editor. If the font is too big for you set it to something smaller with the Options -> Font... menu.
4) Scroll down a bit and look for the lines:
! xlogin*greeting: Welcome to CLIENTHOST
xlogin*greeting: Login as virtualbsd / virtualbsd
5) You can set the message to whatever you wish, but for now lets put things back to normal. Change the same lines so they become:
xlogin*greeting: Welcome to CLIENTHOST
! xlogin*greeting: Login as virtualbsd / virtualbsd
6) Quit mousepad and save when prompted to do so.
7) Log out to verify that the message has changed.