In simple terms the Hardware Abstraction Layer controls many devices in Ubuntu
and
allows you to read and write to these devices. If your friend inadvertantly
downloaded an
upgrade to the HAL and it failed as mine did than you won't have any control
over your
apps, network, and files. He may not be able to backup his files either. Not
knowing
anything about your friend's machine it's far easier to reinstall and watch out
for HAL
upgrades.