EG Free Antivirus 2018
USB Mass Storage:
The USB mass storage device class (also known as USB MSC or UMS) is a set of computing communications protocols defined by the USB Implementers Forum that makes a USB device accessible to a host computing device and enables file transfers between the host and the USB device.
Every user on your network has the ability to walk away with any file or directory he or she can read. Even if the file is too big for a floppy and the user doesn't have a CD writer or ZIP drive, your data isn't safe.
Users can walk away with data at any time with a USB storage device. These key-sized devices offer storage capabilities ranging from 32 MB to more than 1 GB.
USB devices have become extremely popular, and they allow Plug-and-Play (PnP) installation with no user or administrator intervention required. Generic signed USB storage device drivers are part of the installation when you load your systems, and they're ready when users plug in their storage devices.
So it is extremely useful to block USB device on some occasions.