iCloud is also used to store and transfer large attachments sent from Apple's iCloud email addresses.

iCloud also stores a backup of the apps and data on your iOS devices, and — in case your device is lost or stolen — iCloud.com allows you to track your iPhone's location, as well as send a message to display on the device, lock the phone, and/or remotely wipe your data.

(iCloud keeps track of purchases through the iTunes store so that other devices have access to the content, but iTunes-sourced music, apps, movies, TV shows and books don't count against your available online storage.)

Apple allows users to buy more storage and pay for it monthly.

Apple's straightforward privacy policy is available online here.

It's a useful service if you move from device to device, and is supported in a variety of built-in apps, including Mail, Safari and Apple's version of the Microsoft Office suite (Pages, Numbers and Keynote).

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