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I'm selling a 4-year-old Dell PC with Windows 10 and two SSDs and I want to be sure that nobody can recover anything from my personal deleted files. So far I've done the following.

  1. Completely Bitlocker encrypt both disks, including unused space. (Note the machine did not have TPM so I had to use a password)
  2. Uninstalled software and deleted all personal files. (For sake of discussion, let's assume I didn't miss any personal files.)
  3. Created a new, Administrator-level account
  4. Logged on to the new account.
  5. Completely deleted my previous user account.
  6. Completely Bitlocker DE-crypted both disks again
  7. Completely bitlocker encrypted and then decrypted both disks, yet again.

My idea was that if Bitlocker full-disk encryption/decryption really touches the whole disk, then two rounds of encrypt/decrypt out to overwrite everything. But I don't know if I understandit correctly or even if SSDs truly work like HDDs in that regard

Is this good enough? Is there some other step I can take that doesn't involve buying some expensive tool?

I can't sell this encrypted and I want to leave Windows 10 on there so I didn't want to completely reformat the system drive.

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    SSDs do not actually allow you to overwrite the whole thing due to overprovisioning space. – forest Jul 29 '19 at 6:40
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Either you're serious about deleting your data, or your serious about keeping your system functional as it were. The distinction between user data and operating system state is kind of weak, especially on Windows' questionable ecosystem with myriads of third-party things that shouldn't be a system service, but are.

You'd want to enable hardware disk encryption, then wipe that password, leading to the SSD safely discarding all data (or ways to decrypt it).

You'd lose your running Windows.

Honestly, when buying a used computer, first step, wipe the SSD and re-install the operating system from clean slate. Have no interest in continuing to run the malware that the previous owner (most likely involuntarily) ran.

So, a "already working" Windows 10 installation adds exactly nothing to the worth of a laptop to me. A Windows License, however, might. So, clearly mark that you're selling the laptop with a windows 10 license, and deliver it with the product key (which, afaik, you can somehow extract from your running windows). You can pre-install Windows if you want, up to the point where it starts asking for customization.

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  • That does sound more reasonable. I just want to give them running Windows 10 so a fresh install is probably the way to go. I've just always had this irrational fear of resetting a PC -- that I'm going to do something wrong and end up with a real brick. (Which is odd because I've reset Windows PCs plenty of times). I'll bite the bullet and go the clean slate route – Joe Jul 28 '19 at 22:06
  • I do have to create installation media though. As long as I've saved the product key, does it matter which Windows 10 PC I create the installation media from? That is to say, is installation media generic or specific to the Windows install from which you created it – Joe Jul 28 '19 at 22:09
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How about copying massive volumes of junk data into the drives and then doing the same procedure all over again? Overwriting can hide your data (even if it is recoverable by any means).

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  • Thank you I did think of that but I could almost never be certain that the overwritten data accomplished the task by truly being written on empty space that previously held deleted files. I would likely have to completely fill the empty space on the disk. Possible but... well again, if I understand how whole-disk Bitlocker encryption works, that should be taken care of. And if I don't... – Joe Jul 29 '19 at 17:50
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Briefly: No, these steps are not sufficient.

I would split it into 2 parts.

1. Preventing deleted files from being recovered.

Use wiping tools. There are many there, free and commercial. If I recommend you particular tools, the post can be flagged as opinion based. Just google for "Windows wipe free space". The most of the such tools create one or more temporary files and fill them with random data until the whole free space is used, i.e. until the disk is full. Then the tools delete these files. This can take long, depending on how much free space you have on your SDD. If you had classified data on your disk and if your buyer is some powerful state agency, you can repeat wiping 3-5 times. Otherwise single wiping is sufficient.

2. Deleting personal data. (which is actually not the direct question, but since the author described it in details, I consider it also relevant)

If you keep Windows installed on your disk, there is no guarantee that you deleted all sensitive information. Pay attention to the following:

  1. There can be information placed under Users\Public, which may be sensitive from your point of view.
  2. There can be some other user account that were created when you installed some software. E.g. when installing some databases or some web servers, a default user accounts can be created to run this software as a service.
  3. Many uninstallers work incorrectly, delete only the executable files, but leave come configuration files and, much worse, leave information on many different places in Windows registry: Not only below "Software" branch in the registry, but in many other places.
  4. Some of your personal information can be stored under the system branches in the registry, not only unter your users branch. E.g. passwords for some software that you installed in the mode "available to all users" mode instead of restricting to your user only.
  5. There can be sensitive data in directories outside of your home directory.
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  • Appreciate the reply but I specifically titled the post about recovering deleted files to limit the topic to that. When I said "For sake of discussion, let's assume I didn't miss any personal files.", I was not kidding. I deleted all such files in all the places you mentioned and far more . I got global temp, I got ProgramData of every app left installed and a dozen other places. I was hoping to learn about the adequacy of the steps I took to prevevent the recovery of deleted files only. Unfortunately, even after your answer and Marcus answer, I still don't know any more about that. – Joe Jul 29 '19 at 17:11

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