In actual there is no user account called root in Ubuntu. A normal user can become root by using the sudo command. But in Breezy, the first user’s password is can be easily found by any user reading the file /var/log/installer/cdebconf/questions.dat. This bug is present only in Breezy (5.10) and not in Dapper(6.04) the yet to be released version.
There are two packages – base-config and passwd which needs to be upgraded to prevent this problem. A standard system upgrade will fix this problem.
If you are upgrading from 5.10 to 6.04 then you need to upgrade your passwd package to the newest version.