This info is from Ars Technica, "There's yet another iOS bug that causes Apple devices to crash when they receive text messages containing a string of special characters. With further finessing, the same exploit may be able to attack Macs, since OS X is also unable to process the same combination of characters, which are technically known as glyphs."
Here's a screen shot of the text that causes iPhones to promptly crash.

Read this article for the warnings and the remedy they suggest: http://arstechnica.com/security/2015/05/beware-of-the-text-message-that-crashes-iphones/#p3