Access User Level Security is "session" based, and it's always on ... when
you open Acces (either directy or by opening an Access database) you ALWAYS
log in through a workgroup file - even on a new, fresh install of Access,
all users log in through the system.mdw file, and all use the same account
(the Admin account), and every database is owned by Admin. Since all
system.mdw files are identical across all similar Access versions, you can
transfer a database to any machine with Access installed and open it.
So when you open a "session" of Access and use the default system.mdw, you
would be able to open ANY database that is "secured" with the system.mdw
file. You would not be able to open any databases correctly secured with
another workgroup file.
If you PROPERLY secure a database, you woudn't be able to open that database
from an Access session opened with another workgroup.
A workgroup file stores Users, Groups, Group Memberships, and Passwords
(encrypted). The database itself stores object permissions ... in other
words, the workgroup file authenticates the user and allows you to open a
SESSION of Access ... once in that session, you would not be prompted for a
user/pass combo again because you've already been authenticated. From this
point, any db secured with the in-use workgroup file could be opened
(assuming your user account had permissions to do so). To change workgroups,
you must close and re-open the Access session - since you didn't do this,
you would NOT be prompted for the user/pass again.
To put it a little more simply - you weren't prompted for a new user and
pass because the user/pass info doesn't "travel" with an individual
database.
Note also that the "database password" method of security (if you can call
it that) travels with the database, so if you set a db password, you would
be prompted for a password anytime you open the database.
As TC suggested, you would be well advised to read and re-read the Security
FAQ, this newsgroup and other resources regarding security before moving
ahead with your project.