Following the upgrade to 9.3 many iPhone users are reporting seeing a pop-up prompt requesting they change their passcode/passphrase within 60 minutes. Not surprisingly, many are concerned this is some kind of scam or malware.
It’s probably legitimate, and the reason it appears is one of three possibilities:
1. You’ve got a Microsoft Exchange email account setup on the phone, and the administrator of the account has set a password expiry period to ensure that users don’t stick with the same password for long periods. This shouldn’t affect the iPhone’s main passcode/passphrase but apparently it does right now, probably due to a bug;
2. Your iPhone is managed, which is probably the case if the iPhone was given to you by an employer or academic institution, and the manager has again set a password expiry policy;
3. It’s just a bug that’ll hopefully get fixed in an up-coming iOS update.
The solution is to follow the prompt and change your passcode. Only do this if you’re subsequently switched out to the Settings app. If you get switched out to a web page then, obviously, what you’re seeing is likely part of some scam and should be ignored. (See the instructions at this posting, if that’s the case.)
Of course, you can always change your passcode/passphrase when prompted, and then immediately change it back to what it was.