some devices show in NAC as "device type" Linux backtrack, but these are NAS systemes. Is there a security hole or is it a false indication?
Manufacturers are QNAP Systems, Inc., ICP Electronics Inc.,TP Vision Belgium N.V...
Most likely those devices are recognized as Linux by DHCP Fingerprinting capability of NAC, their software is built upon Linux perhaps?
The approach assumes that a device asks for certain parameter numbers in DHCP option 55, and NAC stores some patterns which, when matched, let's you know what is the system type.
You can create an override like here: https://getsatisfaction.com/extreme/topics/create-a-extremecontrol-nac-dhcp-fingerprint