Well good discussion on it https://news.ycombinator.com/item?id=18138328

Thank you for your documented insight. In spite of our best intentions, we—as a community—often do judgement mistakes. One thing that I've been meaning to do is to write postmortems about our reaction to some events, and their eventual outcome. This would help us improve the way that we digest information.

One particularly interesting subject to cover would be Bloomberg's alleged “Big Hack”[1]. Between the initial publication and the final denial by all the involved companies, a lot of different narratives have emerged and gained traction here—and most of them turned out to be incorrect.

[1] https://news.ycombinator.com/item?id=18138328

Speaking solely from a position of outside naive curiosity, how does SIM card applet development work, why/where is custom development needed, and what sort of security considerations (are|need to be) taken into account?

For example, I can settle doctor's appointments etc with what looks like a perfectly ordinary card terminal; I swipe my healthcare card and after a long sequence of button-presses by the (very patient) receptionist I get a receipt with the Medicare logo etc on it (this is in Australia). I've always wondered if all the logic to do this is hiding in the SIM card or if the card terminal is also running specialized firmware.

The only bit of related anecdata I can remember was... wait, I don't believe it but I found it, probably one of the more interesting bits of applet development out there: https://news.ycombinator.com/item?id=18140208 (the entire thread is a bit of a rabbithole too: https://news.ycombinator.com/item?id=18138328)