Why are we sharing texts? With ios 7?

Me and my sister have iPhones 4S and I got iOS 7 which she doesn't have and I'm getting all her messages and she's getting mine and it's very frustrating because I know we have the same Apple ID but I don't know it's wrong help?

Same thing is happening to me and my sister! I don't know how to fix it.

Its simple. When you updated your software it asked you how and from where you wanted to send a receive iMessages. You probably had your sisters number and/or email selected and didn't even notice. Now you are getting all her information. You need to go to settings, messages, and go to send and receive and unselect her information. It's also a lot easier if you don't share an AppleID and instead have your own, because when/if whoever you share with decides to change their settings and allow your information to become shared, your privacy goes out the window.