It has come to light recently that there is a text message hack that can shut down any iOS device and there is seemly nothing that you can do about it. Now Apple has released a work around until they can figure out a way to patch this hole in the software.
Here's what Apple suggests you do....
- ask Siri to read unread messages.
- use Siri to reply to the malicious message
- Once you reply, you will be able to open Messages again.
- go to Messages and swipe left to delete the entire thread. Or, you can long press on the malicious message, click on "More" and select delete.
There is a patch coming "shortly" put hopefully this helps for now.