iCloud is a cloud storage and cloud computing service by Apple, launched in October 2011. The service allows users to keep data such as calendars, contacts, reminders, photos, documents, bookmarks, applications, notes, and more in sync across multiple compatible devices (iOS devices running with iOS 5 or later; computers with macOS X 10.7.2 or later; and Microsoft Windows), using a centralized iCloud account. The service also allows users to wirelessly and automatically back up their iOS devices to iCloud. iCloud also provides other services, such as Find My iPhone (to track a lost phone and wipe it remotely) and Find My Friends (to share locations with friends and notify the user when a device arrives at a certain location).

Signing up with iCloud is free, and is simple to perform with an Apple ID. When you sign up for iCloud, Apple grants you access to 5 GB of free remote storage. If you need more storage, you can purchase the upgrade plan. To keep your data secure, Apple forces users to choose a strong password when creating an Apple ID to use with iCloud. The password must have a minimum of eight characters, including a number, an uppercase letter, and a lowercase letter.

iOS devices running on iOS 5 and later allow users to back up the device settings and data to iCloud. Data backed up includes photos, videos, documents, application data, device settings, messages, contacts, calendars, emails, and keychain, as shown in the following screenshot. You can turn on iCloud backup on your device by navigating to Settings | Passwords & Accounts | iCloud | iCloud:

iCloud can automatically back up your data when your phone is plugged in, locked, and connected to Wi-Fi. That is to say, iCloud backups represent a fresh and near-real-time copy of information stored on the device, as long as space is available to create a current backup.

You can also initiate an iCloud backup from a computer by connecting the device to iTunes and choosing the iCloud option. iCloud backups are incremental; that is, once the initial iCloud backup is completed, all the subsequent backups only copy the files that are changed on the device. iCloud secures your data by encrypting it when it is transmitted over the internet, storing it in an encrypted format on the server, and using secure tokens for authentication.

Apple's built-in apps (for example, Mail and Contacts) use a secure token to access iCloud services. Using secure tokens for authentication eliminates the need to store the iCloud password on devices and computers.