The common wisdom with regards to USB-to-serial cables seems to be that one should pick FTDI over Prolific because of all the Prolific counterfeits in circulation. It seems that this is now becoming a problem with FTDI, as well.
Up to now it was not a problem for the end-user. FTDI has decided to change that with their latest driver, which changes the configuration of a "fake" FTDI chip so that it is rendered useless (at least without a bit of fiddling with configuration tools and device IDs on Linux or XP).
I hadn't realized that FTDI had such an issue with fake chips until I read this article. Some of the comments point out that the end-user of the device has no way of knowing whether the chip is genuine or not. Further, as noted above, many in the radio programming community purchased devices touted as having FTDI chips in good faith as an effort to avoid the counterfeits Prolific chips.
Anyway, if you suddenly have issues with your FTDI USB-to-serial adapter, take a look and see if the PID has been changed to 0. If so, then you may have been affected by this new driver.
Sources: - http://hackaday.com/2014/10/22/watch-that-windows-update-ftdi-drivers-are-ki... - http://www.eevblog.com/forum/reviews/ftdi-driver-kills-fake-ftdi-ft232/ - http://forum.arduino.cc/index.php?topic=270175.0