I assume you're on Ubuntu, not something else. What your "friend" tells you is
not possible you must be root to do an update ... I dont know of any update that
could mess with the root password. And if you installed an regular Ubuntu image
you don't need the root password .... Only your own password and use "sudo" to
execute a command as root. I dont know of any "xdisk" for anything else than
modding an XBOX...

Are you sure you can trust this "friend" ? Or was he talking about wireless
security. You must check with the internet cafe what is the WPA key if any.
Ask for any other wireless parameters that you need to know to connect. Do you
have enabled DHCP or Is there fixed IP addresses given to you ? Do you have
yourself any filter/firewall to prevent others to get into your machine via your
wireless network card. I would rather check the wireless network configuration
before messing with any "root password" someone would ask me to modify.