Apple has publicly acknowledged the existence of a bug that may brick the iPhone or any other iOS device when the date is set to January 1st, 1970. According to a dedicated Apple Support
Here’s what Apple writes about the bug:
Manually changing the date to May 1970 or earlier can prevent your iOS device from turning on after a restart.
An upcoming software update will prevent this issue from affecting iOS devices. If you have this issue, contact Apple Support.
In case you don’t know, last week, a new bug was discovered in iOS 9 that may brick any iPhone, iPad or iPod touch with A7 processor or newer after the date is changed to January 1st, 1970. Usual procedures like reset, restore or the DFU mode don’t help, although some users report multiple attempts to unbrick their devices using the DFU mode eventually worked.
Apple is expected to release iOS 9.3 in March, so most likely the fix will be included in this software update. Stay tuned for additional information on the issue.