I wouldn't blame the Chinese. FPGAs are reprogrammable-reconfigurable chips, with JTAG being an interface used from programming/debugging FPGAs and microcontrollers. I am sure these backdoors are designed by the companies in order to be able to keep control of their products when asked by higher authorities in case that they are locked (for example having an on-chip FLASH memory locked and unreadable from the common programmer devices). So these backdoors are there in order that your government (CIA etc) can steal the firmware of the otherwise "locked" devices. Many products of the enemies of the USA are made by using FPGAs and microcontrollers from American companies, so I think it's the other way. It is not random that China made their own series of x86 compatible processors and microcontrollers (FYI they don't have to copy any design, they just have to know the machine language which is freely available in most cases in order to implement the behaviour with a HDL language). They don't want to be victims of industrial espionage.