It may seem like one of those rumors that, while widely reported on, turns out later to have been a bunch of bunk. But this one is true: Send someone a text message with a certain combination of characters, and you can make their Apple device crash and reboot. Effected devices include iPhones, Apple Watches, and iPads.
The problem is caused by texts that have a specific combination of non-Latin characters including Arabic and Chinese, and Marathi. When an Apple device brings up text messages in a banner notification, if will typically add an ellipsis to the message, but the part of the operating systems that handles text messages gets confused and overwhelmed by the set of characters and the modifications caused by the ellipsis and will freeze, leading to operating system crashes. Some have reported that their message app will still be frozen after a reboot.
The offending combination
This is not, however, something that can happen by random chance. The Guardian, for example, went through 50 versions of the text string before they could get it to crash a phone.
Although the headlines have been rather alarmist, the actual consequences of the phenomenon seem to go not further than forcing your iphone to reboot itself. It won't brick your phone. In fact, it seems to be turning up more as an annoying prank than any kind of truly compromising flaw in the technology (although seemingly benign flaws have been used to damage systems before).
And as with a lot of these kinds of technological failures and bugs, workarounds are quickly established. There are several in this Reddit thread on the subject. The most popular one seems to be to send the person who sent the text to you a random photo from your photo app. This will allow you to access your message history. (As above, the bug only happens because of notifications with the offending text string.) Once in your message history you can delete the problematic texts.
Could Apple have seen this coming? Probably not. The very specific circumstances that have to occur in order for the bug to manifest suggest that such an issue was unforeseeable. Nevertheless, Apple has stated that they are aware of the problem and are working on a solution.