Blizzard's mobile Battle.net Authenticator is a handy way to secure your StarCraft, World of Warcraft and Diablo accounts from rampant hackers, unless a major iOS upgrade screws it up. Then you're in for a headache.
Brought to players's attention a couple of days ago on Blizzard's forums, in some cases upgrading from iOS 6-something to the shiny new iOS 7 could result in a reset of the Mobile Authenticator app. Having the app enabled means that every time you log in to your Battle.net account, you must enter the code randomly generated by the app. If it resets, there's no logging in, period.
It's suggested that players log into their account before upgrading, temporarily disable the service, and then re-enable it after the upgrade is complete. Users can also take down their authenticator serial number and restore code, using those to restore the app after the upgrade.
If it's too late to turn back now, you've got two options.
If you're signed up for Blizzard's free SMS protect service, removing the authenticator is just a coded text away. If not, you're going to have to get in touch with customer service, sit in a chat queue, and fax proof of your identity to have the safeguard removed. It's a bit of a pain.
Security can be really inconvenient sometime, but it's totally worth it. I had my World of Warcraft account hacked twice before authentication came along, and wouldn't disable it unless iOS 7 forced me to.