So far, the counterfeiters appear to only be counterfeiting the SSOP version of the FT232RL and occasionally the older FT232BL chip. From what FTDI has seen, there appears to be only one or two ...

In addition to this main processor, the Nano also has another chip on board, the FTDI FT232RL, which handles USB communication as the ATmega328 itself isn't capable of doing so out of the box.