A bug in how iOS 8 renders Unicode is causing Messages to crash or the lock screen to reboot when a specific string is received.
The bug occurs when your iPhone, iPad, or Apple Watch (which runs a variant of iOS 8) receives a message containing the specific string of Unicode characters. Because the specific string can’t be rendered, the app crashes or, including on the lock screen, the system reboots.
Unicode is the standard way to encode, exchange, decode, and render text for most languages around the world. CoreText is typically what Apple uses to render the text, and it appears that the Messages app and notifications that attempt to display the bad string will cause the program manager and windowing system (Springboard) to crash.
It’s possible other apps that render the string in the same way might also be affected.
Apple spokesperson has made the following statement regarding the bug…
We are aware of an iMessage issue caused by a specific series of unicode characters and we will make a fix available in a software update.
In the meantime, to prevent reboots, turn off lock screen notifications for any app capable of receiving the bad Unicode string.
Note: Unless you have reason to believe you’re a target, you probably only need to do this until your friends’ attention span lapses and they move on to the next prank.