There's a few ways to get round it on iOS 6. One method would be to backup your device through iTunes, look at the backup files, open the iMessage database, remove the message and restore the device.
You can perhaps get the offending sender to send more messages or even just a long message and that will move the text off screen and allow you to delete the conversation.
You can also sign out of iMessage, sign in as someone else and sign in again to wipe all past conversations but you may not want to wipe old conversations.
If you want to keep old conversations, it may be possible to setup iMessages on OS X, sync the phone with it, remove the message, wipe the message log on the device by signing out and then syncing them back again.
Hopefully Apple will issue updates for every OS affected and in future, they should run text processing in a separate process if possible so that applications don't crash and offending strings would just cause Core Text to go down.
That program will show the messages and you can delete the offending message and then restore the data back to the iPhone. It's a tedious process though and could result in data loss with some apps that aren't backed up properly. Waiting for Apple to issue updates would be the easiest option. I'm not sure why they are taking so long with this - apparently they've known about the bug for over 6 months.
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You can perhaps get the offending sender to send more messages or even just a long message and that will move the text off screen and allow you to delete the conversation.
You can also sign out of iMessage, sign in as someone else and sign in again to wipe all past conversations but you may not want to wipe old conversations.
If you want to keep old conversations, it may be possible to setup iMessages on OS X, sync the phone with it, remove the message, wipe the message log on the device by signing out and then syncing them back again.
It's been fixed in iOS 7 and 10.9:
http://www.imore.com/what-you-need-know-about-coretext-exploit-can-crash-ios-and-os-x-apps
Hopefully Apple will issue updates for every OS affected and in future, they should run text processing in a separate process if possible so that applications don't crash and offending strings would just cause Core Text to go down.
thank you Marvin.
very helpful.
I don't own Mac but want to keep history of messages (not bad message!)
I have to wait for Apple I think but you are helpful and kind.
You should still be able to do the backup and restore through iTunes on Windows. The backup files are stored in locations listed here:
http://www.iphonefaq.org/archives/97900
In that folder will be an SQLite database, which you'd edit with a program like:
http://sourceforge.net/projects/sqlitebrowser/
That program will show the messages and you can delete the offending message and then restore the data back to the iPhone. It's a tedious process though and could result in data loss with some apps that aren't backed up properly. Waiting for Apple to issue updates would be the easiest option. I'm not sure why they are taking so long with this - apparently they've known about the bug for over 6 months.