I have one counterfeit FTDI IC in a Mega2560. The Windows driver by FTDI bricks it, unbricked it in Linux and now works fine in Linux. I regularly read people still getting a counterfeit FTDI in a cheap USB serial.
Which is why I used the words "reputable source": this has been a problem with Prolifics for a /long/ time... quite a few years before FTDI had their patience tested beyond endurance.
The Linux FTDI utility allows you to do things like writing a serial number to the chip: does that work properly, or it there some other easy way of detecting an FTDI counterfeit?
Just to get some oddments "into the record". I've been tidying up various serial-port code today, noting that very often that was working with an interface chip built into an instrument rather than a conventional RS232 port etc.
I can confirm that at least some of the counterfeit FTDI chips do not have writeable EEPROM: these can be identified in eBay etc. photos by bring serialised as G0370111 on the FT232RL chip, and possibly also by having a beige plastic-encapsulated capacitor next to the USB port rather than a ceramic device.
There must be at least one other counterfeit variant around, since a device with R/O EEPROM probably couldn't be bricked by a Windows driver.
Using Linux I was able to manipulate the serial number on a genuine chip using
https://github.com/yogggoy/ftdi_eeprom_writer , and this leaves me able to locate which device (i.e. /dev/ttyUSBxxx) has a module in a particular role by its serial number... although it's hard work.
MarkMLl