Users collection visibility

it seems to be possible for a normal user "USR1" (non admin and not on special groups) to see other user objects through a service.

I have no rules on the "users collection" permissions that would allow USR1 to "see" other users

In fact, If USR1 logs into the composer, he can see just itself on the users list

But if with a service he calls Users["USR2"].fullName, this entity is visible and returns the fullName prop !

This shouldn't be possible.

What I'm missing ?

I use TWX 8.5