If your iPhone is rebooting or your Messages app is constantly crashing, you might be the victim of a recently discovered iOS exploit. This exploit allows pretty much anyone with a smartphone to send you a text message attack that can reboot your iPhone, as well as crash your Messages app.
Apple is working on a patch for the bug, but it won't be out until the next software update is pushed. Luckily, there are a few ways to get your iPhone back up and running the way it was right now. Check out the tips below, which also includes a way to keep your iPhone from being hijacked in the future by vicious pranksters.
Use Siri to send a text message to the person that sent you the malicious text message. Just bring up Siri, say "View messages" or "Read unread text messages," then respond "Yes" when Siri asks if you would like to reply to the malicious text and send them anything.
Using this method, you'll be able to not only respond to contacts in your phone, but also random phone numbers. Since Apple has yet to release an update, this is their official way of fixing it in the meanwhile.
As soon as they receive the regular text you sent using Siri, you'll be able to access Messages. This will also allow the sender of the malicious text to go into their Messages app, since they're also unable to access their text messages.
From the Photos app, text message a picture or video to the person that sent you the malicious text message. Once they receive the photo, you and the sender will be able to go back into the Messages app.
Send a regular text message to the person that sent you the malicious text message. While you won't be able to access all your messages, sometimes you'll be able to access the thread of the person that sent the malicious text (or your own thread, if you were the sender). In this case, sending a regular text message to that person will fix your crashing issue, as well as theirs.
Delete the thread of the person that sent you the malicious text message, if you're able to access it. Or delete the entire thread of that you started (if you sent the attack to them). This will fix your crashing issue, as well as theirs.
Install Unicode Suppressor from MohammadAG if you're iPhone is jailbroken. To get it up and running, install the tweak using either iFile or iFunBox. This will fix any Messages issues you have, as well as the rebooting bug, and will protect you from any further attacks. Note that it only works with iOS 8 right now.
If none of your shitty friends have done this to you (yet), you can take steps to prevent your iPhone from crashing. One way to do this is by disabling text messages on the lock screen, which you can do by going to Settings -> Notifications -> Messages, then turning off the "Show on Lock Screen" setting.
While your iPhone isn't completely free of issues, it will prevent the malicious text message from crashing your device when it's locked.
Simply restarting your phone won't fix any of the issues, so make sure to try out any of the methods above, or let us know about any other fixes you might have stumbled upon.