Security on a split database

[Francesca]

We have a split database with the back end being accessed by about 10 users
(although rarely all at the same time). We currently have each front end
password protected to stop it being accessed by unauthorised users (I know
it's not very secure).



I want to set up a system of users and groups for security - How do I go
about it? Do I set security up on the back end, or on each of the front
ends, or (somehow) both?



I have set up security on a training course so I am not a complete virgin
but you could think of me as an extreme beginner. Any hints/pointers very
gratefully received.



Thanks