USB Library
Importance of Change the VID/PID

The USB Vendor ID (VID) and Product ID (PID) are special numbers (16-bits each) that all USB devices implement. These numbers are especially important for bootloader operation, since they are the primary identifying numbers that a PC application (such as the HID bootloader host/PC GUI program) needs in order to “find” and connect up to the correct USB device on the bus (a USB root port can have up to ~127 USB devices attached to it, and some means must be used to “find” specific products). 

When implementing a USB device with a bootloader, it is especially important to change the VID/PID value from the original/default value as distributed in the example firmware/PC application, to new values that are unique for your application product line. This is important, to ensure that no unintended host/PC application software can ever unintentionally connect up to your USB device, and reprogram it with an incorrect/incompatible USB firmware image, designed for some other manufacturer’s product. 

The VID/PID values can be modified in the bootloader firmware project by editing the USB device descriptor in the usb_descriptors.c file. Once the value has been modified, the host/PC GUI bootloader program that performs the firmware updating must also be modified, so as to search for and connect up to the proper USB device with the new VID/PID. In the “\usb\device\bootloaders\utilities\qt5_src\Bootloader” host/PC GUI source code, the VID/PID values can be changed by editing the #define VID and #define PID constants (which currently resides in the Comm.h file).

MLA - USB Library Help Version : 2.16
http://www.microchip.com/mla