A recently discovered bug in Apple's iOS can crash and disable the Messages app on all iPhone models with a single text message --- yes, another one. The new exploit was discovered by hacker vincedes3, and requires a special vCard attached to a message, which permanently crashes the Messages app when opened --- restarting the app doesn't work nor does a hard reboot because Messages always tries to open the most recent text, sending the app into an inescapable crash loop.
The vCard that causes this crash has 14,281 lines of code where the average vCard has just around 200-300. The bug currently affects any device on iOS 8 through the iOS 10.2.1 beta.
Apple is relatively quick to fix these issues but thankfully it isn't all that hard to get Messages back working. Along with pointing out the flaw, vincedes3 also shared a link that you can open on an affected iPhone to get out of the crash loop --- it essentially triggers a new message. You can also send a new text message to the victim's phone and opening that through the notification should do the trick.
A similar flaw was discovered in 2015 which relied on a specific series of Unicode characters sent via text message to crash the Messages app and case the entire phone to reboot without warning. The infamous "effective power" bug took the internet by storm as iPhone owners used it to prank their contacts.
Last month a five-second video was being shared online as a prank which caused Apple devices to slow down and eventually become completely unresponsive until a hard reset was performed.