Apple will introduce new versions of iOS and OS X at its annual developer's conference.
Apple Offers Temporary Fix for iOS Text Bug, Says Update's Coming Soon
Apple is aware of an iMessage issue caused by a specific series of unicode characters and we will make a fix available in a software update. Until the update is available, you can use these steps to re-open the Messages app.In addition to Apple's suggestions, there are other possible fixes that have worked for MacRumors in other scenarios. For instance, if Messages was opened in conversation list view you can fix the issue by having someone send you a message or sending yourself a message via Siri or through the Share sheet in any app.
1. Ask Siri to "read unread messages."
2. Use Siri to reply to the malicious message. After you reply, you'll be able to open Messages again
3. In Messages, swipe left to delete the entire thread. Or tap and hold the malicious message, tap More, and delete the message from the thread.