If you have any friends who are particularly mischievous or who enjoy pulling pranks, you might want to not hand them your iPhone anytime soon. It has recently been discovered that by changing your iOS device’s time to the 1st of January, 1970, it will cause your device to brick which essentially renders it useless.
Upon changing the time, nothing will happen at first until your phone is rebooted. Once you try to turn it back on, that’s when it hits the fan. Restoring it from backup or putting it into DFU doesn’t seem to fix the problem. There are some who claim that the problem goes away after 5 hours, while some claim that swapping SIM cards will address it.
However your mileage might vary, but safe to say that there doesn’t appear to be a confirmed fix for this problem. This only seems to affect iOS devices with 64-bit processors, meaning that any device with the A7 chipset (iPhone 5s) or later will be affected by this bug. As to what is causing this problem, it seems that by setting it to the 1st of January, 1970, it causes the internal clock to be set to a negative number.
Obviously there isn’t negative time, which then causes an error, which then causes the phone to crash and brick. We expect that Apple will eventually release an update that will address this issue, but in the meantime we suggest you do not try this for yourselves.