News of this “bug” began circulating on Reddit recently, although what, exactly, prompted people to begin experimenting with changing their date settings to something so far back in time is a bit of a mystery. In any case, you should know that a number of iPhone owners have experimented with the bug, and documented their results via video online. In many, but not all cases, it results in a total shutdown of the device, which can only be remedied by a trip into your nearest Apple Store.
Apple has offered no comment on the bug, and as far as we know, there’s no plan on the books to fix it. Literally the only way this bug can impact a user is if they make the decision to manually set their phone’s date to January 1, 1970. In cases where doing this has not resulted in a total shutdown, there are no firm answers, only theories. Best guess is that when you change the date, the date is converted into a numeric value. Depending on your local time zone, setting your phone to this date (or earlier) will result in a negative date value, which the phone’s OS doesn’t know what to do with, resulting in turning the device into a brick.
Again, two things cannot be stressed enough. First, this isn’t a bug you should be especially concerned about, because second, the only way it can manifest is if you make the decision to set your phone’s date, which is a thing you simply would never have a reason to do. Still, it’s a curiosity, and an odd fact worth knowing!