Why 'Erase All Content and Settings' on iPhone can not Erase iPhone data permanently

Before selling your old iPhone 5s or iPhone 5,and buy a new iPhone 6, iPhone 6 plus.You must to erase all data from iPhone permanently before selling old devices,to delete data on iPhone permanently and even never restore them,you can not rely on 'Erase All Content and Settings',because some data recovery software can recover them back easily.In additional,if you want to erase iPhone data before selling,you can learn this use guide Permanently Delete Everything from iPhone Before Selling

Why 'Erase All Content and Settings' and “Erase iPhone data” on iPhone can be restored easily? You need to understand these insider:

Understanding 'Erase All Content and Settings' on your iPhone:

You can remove all settings and information from your iPhone, iPad, or iPod touch tapping "Erase All Content and Settings" in Settings > General > Reset.

Erase All Content and Settings

To erase all content and settings from your iPhone, iPad, or iPod touch:

1.If you wish to recover the data again, ensure that you have an iCloud or iTunes backup and that it is up to date.
Tap Settings > General > Reset > Erase all Content and Settings.

2.When you select to "Erase All Content and Settings," the process can take from a few minutes to several hours. The time this process takes will vary by iOS device:

#Devices that support hardware encryption: Erases user settings and information by removing the encryption key that protects the data. This process takes just a few minutes.

#Devices that overwrite memory: Overwrites user settings and information, writing a series of ones to the data partition. This process can take several hours, depending on the storage capacity of your iPhone or iPod touch. During this time, the device displays the Apple logo and a progress bar.
Note: If possible, connect your device to a charger and leave it connected until the process is complete.

Note: All devices that support iOS 5 or later use hardware encryption.

Learn more:
If you run out of power or reset your device before it is complete, you will see the Connect to iTunes screen after you connect to power again. If this happens and you want to ensure that your content is fully erased:

However,to delete iPhone data permanently,you need to use a iPhone data eraser software,which allows you wipe contacts, text messages, photos, videos and more from iPhone 5s, iPhone 5 permanently.

Restore the device using iTunes.
Connect to power.
Select Erase All Content and Settings again.
Find information about erasing your iPhone data remotely.