Great advice serfty, though I thought it should be fairly obvious. I have heard of cases before of PNRs being used and people performing malicious changes or the like. Whilst I can't remember specific stories, most of the solid stories I've heard are usually related to vindictive ex-partners (particularly those travelling on an itinerary) cancelling itineraries or changing flights (e.g. dates). I've heard of (but can't remember how it is done) people losing control of FF accounts or the value (miles or dollars) of whole booked itineraries (i.e. without actually coercing or threatening the victim).
FF numbers should be carefully controlled as I'd reckon it wouldn't be hard to take control of a FF account (viz. by calling the airline, pretending you are the person or agent of that person, and claiming that you have forgotton your PIN, then you just need to answer some personal questions, which also would not be necessarily too difficult to answer (e.g. birth date, mailing address, recite the last 6 flights you've flown against your account, or any present bookings)). Especially since (maybe not so much in the USA) many airlines take a very frivolous view of the value of one's miles, they would not be quick to act if it so happened that miles "fraudulently" disappeared from your account and thus would not have any strong protections in place (cf. your bank account and if a large amount of money suddenly "disappeared" from your account for no reason, or from another country).
That said, the OP in the quoted FT post is an idiot to think that they have an action against UA, unless it can be comprehensively proven that UA actively contributed to the errant action or "fraud". The OP even contradicts themselves within the thread with respect to the "privacy" issue and access logistics. I'd say lesson learned, stop annoying UA (and FT) and, if so be it, go get the gun out (it is the USA after all)....
