USB drives showing to all thin client users

[myschool]

Our university has implemented Multipoint Server 2011 (soon upgrading) with Ncomputing L300 thin-clients for all students and faculty. Everything runs smoothly, however, we are seeing an issue where plugged in USB drives are appearing to all logged-in users opposed to just the user plugging into their terminal. As you can imagine, this can become a serious issue where students are able to view faculty data and vice versa. Even a plugged-in smart phone has appeared on the network. Where can we modify this setting so that drives do not appear for all users?

We currently utilize Active Directory and users plug their flash drives directly into the L300 Thin-clients. USB usage must continue to occur because students need to save assignments and they print often but this is a major security issue.