Thanks for your patience!
Due to an issue with the latest version of the iPhone Battle.net Mobile Authenticator application (version 1.3.0), we've temporarily taken down the app from the iTunes store. Rest assured that we're already working on a new version and will be providing an update in this thread as soon as that new update is up. Please note that until the new version is made available, iPhone and iTouch users will be unable to download the app or upgrade it to the latest version.
If you use a non-iPhone version of the Battle.net Mobile Authenticator, have not upgraded to version 1.3.0, or if you upgraded an existing version via iTunes but have not retrieved a new serial number, your Mobile Authenticator should be unaffected by this issue and continue to function as normal. Regardless if you retrieved the update or not, there is no security threat or risk associated with the Authenticator's ability to continue protecting your account while attached.
As always, if you are experiencing any issues with an Authenticator or Mobile Authenticator, we encourage you to contact our customer support staff for assistance - https://us.battle.net/support/en/ticket/submit