IShredder is a curious app. It claims to securely erase the files on your iOS device using better-than-military grade algorithms. The idea is that you can then sell your device without leaving sensitive data behind.
The problem is that this is already built in to iOS.
If you ever reset your iDevice using the “Erase All Content and Settings” feature, you will have been surprised at how fast it wipes up to 64GB of data. This is because everything on your device is encrypted, and is decrypted on the fly as you use it. It’s similar to Filevault 2’s whole-disk encryption on the Mac, and it is invisible to the user.
When you reset your iPhone, the disk is not wiped. Rather, the decryption key is destroyed, leaving you with nothing but the OS and a disk full of encrypted mumbo jumbo.
What iShredder appears to do is overwrite all free space on your device with random data, zeroing it out several times over. But as it is available in the App Store, it has to work like any other app. This means no access to data stored by other apps, and also that it itself acts within the encrypted disk of your device. This means you’ll need to delete all the files first, and I guess all the apps on your iPhone or iPad, in order to give iShredder free run of the disk.
To sum up then: If you are paranoid enough to remove your data and overwrite it before deleting the key to your iDevice and leaving it full of encrypted nonsense, but not paranoid enough to actually use a computer and special tools to really go to town on the iDevice’s drive, then this may be for you. There is a confusion of versions available, from “standard” through “Royal Premium” up to “Enterprise,” showing that this is clearly aimed at Windows-minded folks.
Good luck clearing that porn off your machine!