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So far as we are going through the course we interacted with the file system quite often.

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We also learned how to download and upload files how to share files securely with friends and contacts

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how to remove metadata that can be used to anonymize us or get information about us.

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So before moving to the next section I think there is still one missing piece which is how to properly

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delete files and wipe storage media.

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Now in general and operating systems when you right click a file and deleted or even if you shift deleted

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and empty your recycle bin or your trash the file doesn't actually get deleted.

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What happens is the operating system marks the file or marks this piece that the file was occupying

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on the storage device as available so the data of that file will still exist on your storage device.

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Until that space is overwritten with other data.

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That's why we see so many tools that are very easy to use that you can use to recover deleted files.

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Now these are very simple tools that you can download from the Internet for free so you can only imagine

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what a resourceful adversary can do so because deleting a file doesn't actually delete the content of

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it or its data unless it's overwritten with other data.

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There are tools that randomly fill up that piece of that file with random data so that it's more difficult

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to recover that file.

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Now tells comes with such tools pre installed as you'd expect.

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So if we go through our file manager and go through the file that we want to delete.

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So in my case it's in files and it's this image right here.

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Now I can right click the image and just click on move to thrush which will literally just move a toothbrush

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similar to any other operating system.

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And then I'd have to go to the trash right click and empty.

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And like I said this will still not delete the content of this image or the data of this image from

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my storage.

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The better option to go to if you want to security remove this file is to click on wipe right here.

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Now if you click on that and expand the options in here you'll see that it will ask you for the number

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of passes of random data that will be executed to override the location that contains the data of this

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image.

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So by default this is set to two which should be good enough for most hard disks.

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You can set it to 38 for all ones or one which is not very secure which will only protect you from the

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very simple software that you can download on the Internet.

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Now this method will work on hard drives but it won't work on U.S. beef steaks or solid state drives.

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Now if you don't know the difference between hard drives and solid state drives then I highly recommend

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you go and do some reading on that.

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I will include things in the resources of this lecture.

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But basically the way that solid state drives work they don't have sectors.

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They use cells in order to store your data.

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And even if we use a tool similar to this tool right here in order to override a specific location of

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this solid storage device the logic inside this storage device will probably overwrite the request that

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we make in order to increase the life of the device.

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Therefore you might use this click on wipe and think that it works but it might actually not work as

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you would expect it.

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So you can only properly rely on this method if you're using a hard drive and not a solid state drive

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or a US b device.

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Now that's for removing one specific file.

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Well what if we wanted to clear all of the free space or all of the available space on the system.

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Now this is only relevant if you're using persistence obviously and you might want to do this because

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you've deleted a number of files insecure lives so by literally moving them to trash and emptying the

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trash and then the contents of these files like I said will still be recoverable from your storage device.

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Therefore what you want to do is you want to right click any empty space in your file manager click

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on WIP available disk space and you'll get a very similar window to the one that we just got with the

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same options.

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And once you set the options you click on wipe and still clean and that'll securely clean the available

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disk space so it won't delete the files that you have.

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It will only clean the available disk space filling it with random data to make sure that it can't be

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used to recover the files that you deleted.

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So it will only clean the files that you deleted.

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It won't affect anything that you already have on your storage device that you did not delete yourself.

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Now this is great.

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But again it won't work as expected when it comes to solid state devices anti US devices for the same

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reason that I mentioned earlier.

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Therefore if you're using a solid state device or a USB device and you want to securely delete all of

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the data that you have on it then you have two options.

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First option is physically destroy that device so you can burn it put it in a microwave do whatever

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you want really.

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Or the other option is to securely format the device and wipe it and I'm going to show you how to do

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that in the next lecture.