Battle.net members with a mobile authenticator on an iPhone, iPad or iPod, listen up: Today's iOS 7 update may reset your authentication info. Blizzard has a few suggestions to make sure you're still protected after the update hits:
Write down your authenticator's serial number and restore code, and restore it to your phone after the update
Remove the authenticator before updating and reattach it after iOS 7 is installed
Use Blizzard's SMS Protect, a free service that can remove an authenticator from your account
Update via wi-fi, since this reduces the risk of an accidental reset altogether
Read through the mobile authenticator troubleshooting page for specific questions, and enjoy that fancy new version of iOS.