Apple has issued to address a battery drain bug, introduced in iOS 6.1, caused by excessive network communication with Microsoft’s Exchange Server; the server also suffers from excessive log growth, and significantly increased memory and CPU use that hurts performance. As you can imagine, both iOS users and Exchange Server admins were extremely unhappy about this bug.
What may be confusing is that the problem is described in very different terms by Apple and Microsoft. In a support article,:
When you respond to an exception﹡ to a recurring calendar event with a Microsoft Exchange account on a device running iOS 6.1, the device may begin to generate excessive communication with Microsoft Exchange Server. You may notice increased network activity or reduced battery life on the iOS device. This extra network activity will be shown in the logs on Exchange Server and it may lead to the server blocking the iOS device. This can occur with iOS 6.1 and Microsoft Exchange 2010 SP1 or later, or Microsoft Exchange Online (Office365).
﹡An exception is a change to a single instance of a repeating calendar event.
This is real — we recently saw a warning from Cornell Information Technologies to their iOS users about the problem, and Apple is clear about how iOS 6.1.2 resolves the bug.
However, while both referencing Apple’s support article and saying that iOS 6.1.2 resolves the issue, Microsoft talks about it from the perspective of the Exchange Server admin, and in completely different terms.:
When a user syncs a mailbox by using an iOS 6.1 or 6.1.1-based device, Microsoft Exchange Server 2010 Client Access server (CAS) and Mailbox (MBX) server resources are consumed, log growth becomes excessive, excessive growth in Recoverable Items may occur, and memory and CPU use may increase significantly. Server performance is affected.
Additionally, Office 365 Exchange Online users receive an error message that resembles the following on an iOS 6.1 or 6.1.1-based device: “Cannot Get Mail. The connection to the server failed.” The only option available to users is OK.
Apple is talking about changing a single instance of a repeating calendar event, whereas Microsoft is talking about syncing a mailbox. But according to Exchange-savvy people we talked with, this makes sense, since from Microsoft’s perspective, working with a calendar event does involve syncing a mailbox. on his blog.
Even though this seems like a bad bug for both users and admins, if you use an Exchange Server at work for email and calendaring, we recommend checking with your server admin before updating. He or she will probably recommend the update, but it’s best to coordinate. If you’re not using Exchange for calendaring, you can hold off on this update, under the rubric of not fixing that which isn’t broken.
This is the second patch that’s been issued to fix a problem introduced in the release of iOS 6.1 (see “,” 28 January 2013), with iOS 6.1.1 released two weeks later to fix cellular connectivity problems on the iPhone 4S (see “ ,” 11 February 2013). Additionally, iOS 6.1 introduced a bug that enabled someone to  and see contacts and photos. Apple’s release notes (well, note, singular) for iOS 6.1.2 don’t mention a fix for this exploit, and  confirms through its own testing that the update doesn’t patch this security hole.
The free iOS 6.1.2 updates are available through iTunes as a full download (989.5 MB for the iPhone version and 1.08 GB for the iPad version), though you can drastically save on the download size by updating via the over-the-air option on your device (go to Settings > General > Software Update). The over-the-air delta for the iPhone is 12.8 MB and just 12.5 MB for the iPad update. The update is free, and it can be applied to the iPhone 3GS and later, iPad 2 and later, and fourth-generation iPod touch and later.