A new bug in Apple’s mobile operating system iOS could cause iPhones or iPads to crash permanently — though it does require users to manually reset the date to January 1970.

The bug was first revealed in a video on YouTube by Zach Straley, which shows an iPhone 6 crashing simply by resetting the date. It takes quite a bit of scrolling in the Settings menu to reset the date as far back as January 1970 but once you do, and you reboot your iPhone, the device won't come back on.

Chance Miller, a reporter for 9to5Mac, carried out a similar test on his iPad Pro and successfully managed to permanently crash his tablet. The reason why this happens is still unknown and Apple has yet to respond to a request for comment on the issue.

According to a Reddit thread on the subject, the best guess of why this happens is that it has to do with time zones and that setting the date to Jan. 1, 1970, causes the internal clock to be set to less than zero, which confuses the device and crashes it.

The problem only affects iPhones and iPads using 64-bit processors, which means any device using the A7, A8, A8X, A9 or A9X. So all iPhones from the 5s up to and including the iPhone 6s and iPhone 6s Plus will be vulnerable while iPads including the original Air and newer versions are also affected. The bug has been shown to work on all versions of iOS from 8.0 to the current version, iOS 9.3.

Some users on the Reddit thread say they have experienced the same problem simply by changing the time zones, while someone on Twitter has pointed out that the default reset date when iPhone batteries are replaced is Jan. 1, 1970. 

There doesn't appear to be an easy fix for this problem at the moment. Putting the crashed iPhone or iPad in device firmware upgrade (DFU) mode and getting iTunes to recognize it will work, but you won't be able to get the device to move beyond the boot screen. One Reddit commenter suggests that replacing the SIM card will fix the problem, while another suggests the device will simply reboot after around five hours.

For users worried that someone with access to their phone could decide to reset the date to Jan. 1, 1970, one developer has created a tweak to prevent this from happening — though it will only work with jailbroken iPhones.