A newly-found bug in Apple's Safari software causes any iPhone or iPad to slow down and then crash when a specific video file is played in the browser.
Discovered on Reddit, the nonsensical five-second video must apparently contains some kind of corruption or irregularity in its mp4 file. If played in Safari (from a link sent in an email or text message, for example), the device will continue to function as normal for around 10 seconds before becoming sluggish and eventually being rendered unresponsive.
![The mp4 video that causes iPhones to crash when viewed in Safari.](/web/20170503083139im_/http://www.theage.com.au/content/dam/images/g/s/v/e/m/u/image.related.articleLeadwide.620x349.gsvel6.png/1479859548968.jpg)
Fortunately the video shouldn't be a cause for panic among iPhone users. Even if you do click on the link and freeze your phone, simply restarting it (by holding the power and home buttons for a few seconds) will restore it to normal function.
The exact cause of the glitch isn't entirely clear, however given that the video appears to play fine in other software, and given the behaviour of gradual slow-down, one would assume that playing the video sends Safari into a loop that causes it to use up more and more of the device's memory until it crashes.
As with other similar exploits in the past (the string of text that disabled iMessage, the specific date that temporarily bricked iPhones if set as the current date), it's expected that Apple will eventually roll out a fix now that this issue has surfaced. At present the glitch appears to affect just about all iOS devices, as seen in the video below from YouTube channel EverythingApplePro.
On certain older devices or software versions, watching the video leads to an immediate shut down.