I just got the clone arduino UNO from China, but device manager cannot recognize the USB driver from official arduino IDE 1.6.5 software package.
I'd like to post the solution, hope it helps.
You need to download the USB-Serial CH340 driver.
(I got from this link USB-SERIAL CH340 Drivers Download for Windows 10, 8.1, 7, Vista, XP) It works fine.
In Windows --> Control Panel --> Device Manager --> choose your unknown USB device.
Then you browse the USB-Serial CH340 driver.
Everything should be fine!!