Thanks Paul it is much clearer now.
A few points still remain unclear to me:
* I design a database and grant access to a user other than SYSDBA e.g.
MASTERUSER
When the user installs FireBird they don't have a user MASTERUSER, so they
won't
be able to connect before SYSDBA creates MASTERUSER.
BUT should I give the SYSDBA password to the DBA of the one system, he can
also
access the data on different systems, hosted on the same machine. He can
also
change the passwords for other systems. Should I not give the SYSDBA
password to
anyone and handle user management myself?

* When the database is backed up, should security.fdb also be backed up to
make sure
that the user information aren't lost?

* Would a better solution be to have a single user which everyone uses to
log in and
a seperate USER table to validate user etc. This would mean that every
user can
have the same username for every different system.

Regards
Alfred Thomas