The video is a seemingly harmless mp4 file showing what appears to be a very quick magic trick.
Phones are reported to continue working fine for up to 10 seconds before then slowing down and eventually crashing.
It’s not entirely clear why the video has such an effect but it’s thought the file is corrupted or possibly encoded with a malicious bug.
Luckily, there doesn’t appear to be any long-lasting effects and the bug can be fixed with a hard reset. This is done by pressing and holding the power button and volume down button simultaneously for iPhone 7, or the power and home button for all other iPhones.
Similarly, in 2015, a text message bug caused iPhones to reboot if received.