However, that will strictly return the user name of the currently logged on
user at the machine where it's run: it will not return the list of the (say)
4 users who are currently using the backend database according to what's in
the ldb file. (And, to be honest, I always cringe when someone suggests
using the UserName environment variable, given how simple it is to reset.
http://www.mvps.org/access/api/api0008.htm at "The Access Web" is a far more
reliable approach)

It's actually a very non-trivial activity to know who's logged onto a given
machine. http://www.mvps.org/access/api/api0062.htm shows one approach, but
I'm not sure that will work in all environments (I'm not sure whether the
machine's Access This Machine From The Network property matters, nor do I
know whether the code needs to run in Admininstrator mode)