Go to manual setup, disks, file sharing..
In the area Secure Shared Disks.. you can choose with accounts.
Select that option and a warning comes up.. take special note of that warning. It is exactly the issue I explained that you are likely to lock yourself out of everything.
A new tab will then appear.. accounts.. you can then create any number of accounts. Each account will be able to access only the files of the person who logs on with those account details.. and it will lock you out of everything that already exists on the TC.. I have to confess I did not pursue it futher to see if I could then get access.. I do not live in a situation where I need that level of security. But I think most people do not know it is there or how to use it. The obvious point to do this is when you first setup the TC.. not after a couple of years of use.
Now doing a quick google there is very little info out there about this. And Apple don't exactly fill their manuals with detailed info of all these hidden extras.
This post suggests the USB is not covered by the setting.
http://forums.macrumors.com/showthread.php?t=1081023
But that might be due to the USB being added after the accounts have been setup. If the accounts are setup with the USB connected it should be covered.
Experiment and tell us.
I don't think even Pondini has any help for us.
It has come up a few times in the discussions but generally people are not too worried about it. The TC is a home use device and so people generally don't need or even want a heck of a lot of security.. TM itself keeps things separate and it isn't easy to look into other sparsebundles. Not impossible but not easy.
Always remember the TC in the end was designed as Time Machine backup device.. not a NAS.
https://discussions.apple.com/thread/1420302?start=0&tstart=0
