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How to permanently erase a file from disk to make it unrecoverable.

There are true negative situations where we normally consider a file has been deleted and is unrecoverable in Windows but there's a good chance that they can be easily recovered by using data recovery software (also known as undelete utility). Since normal computer users are unaware that the deleted files still remain accessible, deleting files insecurely could result in privacy concerns or stolen data by a third party.

Consider the following actions we normally do when deleting files.

  1. Empty the Recycle Bin.
  2. Format the disk.

Files (if not all) deleted in these 2 ways can be recovered easily if you recover the files in a timely manner, because Windows only removes the link to data or the files storage area on disk has not been securely overwritten by other files or means such as formatting disk.

So the question is how you can permanently erase a file from disk and make it unrecoverable by data recovery software? This question actually should be broken down into the following two sub questions.

(1) How to permanently delete an existing file.

(2) How to permanently erase a file that has already been deleted (it does not exist in recycle bin anymore and is hidden in file system unless you scan the disk by data recovery software).

Nowadays, many experienced computer users are award of the answer to the first question. To permanently delete an existing file, there are many erasing software that can help overwrite files multiple times or passes. One such good software is Eraser from the Open Source community SourceForge.

In this article, we're going to go through the steps to address the second question.

In a nutshell, here is what we are going to do. I'll format my USB thumb drive so all the data on it are supposed to be lost and the full size of the USB disk is available for reuse. Then I'll use a data recovery tool to scan the empty USB drive to get a list of deleted files (and as such, they are hidden in Windows Explorer). This way, the deleted files can be either recovered or securely and permanently erased. For this article, I'll choose to erase these hidden files.

1. Select the drive to format.

In left hand side pane of Windows Explorer, right click the driver letter F (my USB disk) and select Format...

2. Format the USB drive

Then click Start to perform the format.

3. Format completed.

Now the USB disk has been formatted and all the data on the disk has been removed. Next we will want to recover files from this formatted disk.

4. Run the recovery software to scan the formatted disk for hidden, deleted files.

Recuva is a free, powerful, and very comprehensive tool for data and file recovery.

After you have downloaded and installed Recuva, run it.

5. Select the file type to scan.

Select the last option on the list so that we can manually select the disk to scan.

6. Browse to a specific location which is my USB F disk.

Click Next to continue.

7. Ready to start.

Select Enable Deep Scan checkbox. A shallow scan won't find any files on the disk that has been formatted. Click Start button to continue.

If you forgot to enable deep scan, the software will ask you to confirm.

8. Scan in progress.

Dependent on the size of the disk, sometimes it could take quite long time to deeply scan a large disk.

9. Scan completed

After the search is completed, Recuva lists all the files it could find, together with other information about each file.

10. Choose the deleted files to erase.

Because most of the original filenames have been renamed, if you are unsure which file(s) to erase, select the checkbox at the top of the first column. It will automatically make all checkboxes selected so that the software can erase all the files.

Here we only select one file [000819].pdf to permanently delete. In the State column for this file, you can see that it's still in Excellent state which means it can be recovered to its original state and that's why we should not trust and rely on disk formatting to remove sensitive data on a disk when discarding an old disk.

11. Permanently erase the deleted file.

To get rid of the file forever, either tick the checkbox or highlight the filename. Either way, right click in the cell of the filename, then in the pop-up context menu, select Securely Overwrite Checked or Securely Overwrite Highlighted.

Then you will be prompted to confirm if you want overwrite this file. Click Yes to continue.

The file has been overwritten and is unrecoverable.

After the overwritten, the State of the file was immediately changed to Unrecoverable.

So far so good - all the hidden files have been permanently erased (or overwritten) on my formatted USB disk by the security software Recuva. So can we now 100% certain that no files can be recovered by some high-end security applications? It's not guaranteed. To gain some extra peace of mind, I'll want to physically destroy the USB disk to make sure that data is completely unrecoverable. But I'm not going to really do that as I don't have any sensitive data on the disk and I still need it for my next project.

Happy Erasing!


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