Right, this is my first post but I have been lerking for a few months now, so I am a major tuning noob, I'm slowly learning about all the bits.

however I have been told that I can't use say a mates med9.1 file on my med9.1 car (both mk5 GTI) due to immo data? But I accidentally flashed his file to mine (before I was told this) and it ran fine, so now I'm confused as hell, what I may be asking is aslong as the hardware, software and ECU part numbers are all the same could I use any file I damn please?