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Shredders or Secure Delete tools actually address two distinct problems, only one of which applies to Flash. Addressing the other could be harmful.
I have a question regarding file shredder software and its effectiveness when used on flash drives. I recently tried to shred some files on a flash drive. I applied various aggressive shredding methods - 35 passes, 7 passes, 3 passes, etc.. Each time, using a relatively old recovery software, I was able to easily recover most of the supposedly shredded files!
Are these shredder softwares not intended for use on flash (solid state) devices? If so, why not? Are they effective only on hard disks devices?
I will say that I'm surprised that the file recovery tools were able to recover files after being shredded. I would have expected the files to be gone.
Using a file shredder on a flash or solid-state drive isn't something I recommend doing, at least not in the same way as you might on an actual hard disk. The problem is that you could be wearing out the flash drive faster than you need to.
File shredders, or secure delete utilities, address two distinct problems when you delete a file in Windows:
When a file is deleted, the data is not actually overwritten.
On magnetic media, data that has been overwritten might still be recoverable using advanced (and expensive) forensic tools.
Flash drives are not magnetic material, and hence the second item simply doesn't apply. When data is overwritten, the previous data is gone. There's no "magnetic residue" to use to perhaps recover the previous data.
The approach that file shredders use to really, truly, positively erase data on magnetic material such as hard drives is to overwrite it multiple times with random data or data patterns that are designed to make any previous data completely unrecoverable. In reality, overwrite the data two or three times, and for all practical situations it's gone. 35 pass shredding is overkill for the seriously paranoid.
And regardless, overwriting more than once is only applicable for magnetic material.
The problem is simple: flash memory wears out the more you write to it. So writing to the entire flash drive 3, 7 or heaven forbid 35 times when in fact you only needed to write once could be seriously shortening the useful life of that device.
So my advice is simple: to shred or securely delete the data on a flash or solid state device, use a utility that will perform exactly and only one pass of overwriting the deleted data.
That'll be enough.
And if the tool you choose isn't working, I'll point you to SDelete, Secure Delete, which will let you do exactly that.
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