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It is important to understand that applications must be specifically designed to utilize data protection. Do not store or use sensitive data with applications that do not make use of data protection. More information regarding this feature is available on Apple's site at iOS 4: Understanding data protection. iOS 7 greatly expanded the use of data protection to encrypt all application data by default, and as such therefore is strongly recommended.
It is strongly advised that, in addition to enabling data protection, all iOS users read the Apple iOS Hardening Checklist and follow all of the recommendations therein.
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