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We all know that if you want to completely delete files from HDD, you have to use a special erase algorithm in order to make it impossible to read it back. But what with the memory cards? Do they need the same algorithms to ensure that no one could read it back? (it has a completely different structure to store data, and I don't know what the case here with secure delete)

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Plus addon to my question: Memory cards do not delete the data if you press delete on the files, it just updates the flags belongs to the deleted files. However if I use a program to put zeros on that location, will it completely delete the card's content? Plus add-on: HDD-s do not need nowadays to wipe or secure delete them more than once. A simple delete with filling zeros would enough because today's HDD are very crowded and there won't be any ramining magnetic "info" after you delete it. –  daveny Dec 11 '09 at 13:05

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Securely deleting from a memory card is often much more difficult than from a hard drive. Because solid state memory cards fail a lot earlier than a hard drive if you write data over a single bit repeatedly, many of them dynamically move data around in a manner transparent to the computer. Thus, when the computer thinks it's writing over the same part of the disk, it's actually writing to a different part to avoid excessive load on the same disk.

My ideal solution would be to use something like TrueCrypt on the whole drive; then, without the password, the disk is useless anyway; there's no need to securely delete files as unless you have the password all that could be recovered from the disk would be garbage.

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As memory cards are a form of magnetic media, I would imagine that the same rules that pertain to hard disks would also apply here.

So I would say that securely deleting a memory card requires a wipe algorithm.

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I thought memory cards are a form of electronic media. Or not? –  daveny Dec 11 '09 at 12:51
    
"Flash memory is a non-volatile computer storage that can be electrically erased and reprogrammed. It is a technology that is primarily used in memory cards" - Wikipedia –  daveny Dec 11 '09 at 12:52
    
@daveny: You're right and I used the wrong term. However I still say that any media supporting rewrites can probably be recovered by the right tools. So I would counsel wipe. –  harrymc Dec 11 '09 at 13:11

You can recover from most formats as when you delete, you dont actually remove the information, you remove the inodes used to locate the information. Using a piece of software like PhotoRec you can recover data even if the inodes are deleted.

If you need to make sure a drive is unrecoverable, you should use a tool like the HDDguru Wipe tool for Windows, or if your using a *nix/BSD operating system your can just use dd if=/dev/urandom of=[your drive here]

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