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I've got a set of computers that have had privileged information on that I want to be able to re-use. If I used a Windows boot drive to re-install Windows, how sufficient would that be towards keeping the old data safe?

I'm aware that the only sure way to secure the data is by grinding the hard drives (HDD for my purpose, but for the sake of a more useful reference, if there's any difference for an SSD I'd like to know that too) into a fine powder, but how 'good enough' is it? If it's not good enough, is there an alternative that leaves the hardware intact that is functionally good enough, assuming that incredibly powerful people don't want my data, who'd just break out the pliers and get it anyway.

I don't have any particular threat model - I'm talking about handing over the hardware and never looking at it again, and honestly don't know how to construct a threat model. There would be legal ramifications if the data could be recovered, if that helps address the "how worried are you" kind of question in the comments.

Extra points that I'm interested in, but are tangentially related to the question so aren't required for an answer is; what other issues am I likely to run into if I were to give/sell these computers on? (My organisation owns the computers and the licences for Windows, and would like to offer them to employees once we're done with them). I believe there's an issue with transferring the Windows licence, for example.

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  • 3
    After re installation overwrite all free space then you are good to go....howtogeek.com/137108/…
    – Moab
    Sep 21, 2018 at 18:50
  • 3
    You do understand you can just Reset Windows 10, choose to keep nothing, and and you will get the results you want? If these are Enterprise editions, it will be more difficult, for the new owners since they won’t be able to activate them due to loss of the KMS. Volume licenses must communicate with the KMS once every 180 days.
    – Ramhound
    Sep 21, 2018 at 18:51
  • 1
    Once old data is overwritten by re installation and free space overwrite, nothing can be recovered.
    – Moab
    Sep 21, 2018 at 18:51
  • @Moab That sounds like an answer to me, pulling the contents of that article into one would get my upvote :)
    – Yann
    Sep 21, 2018 at 18:55
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    @Yann - So instead just install Windows with the generic key, and leave it to the new owner, to change the license key. I personally would, encrypt the data with BitLocker, then just format the HDD and reinstall an unlicensed installation of Windows. This makes data recovery impossible and the burden of getting a license somebody’s else problem
    – Ramhound
    Sep 21, 2018 at 18:59

5 Answers 5

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Create a DBAN USB or CD and wipe the drive. This utility is designed to wipe a hard drive by overwriting it. DBAN only works on hard disk drives (HDD), not solid state drives (SSD).

You do not need to do a multipass wipe. A single pass is all you need to prevent others from reading your drive. The 7 pass wipe is a myth that still persists to this day.

Reinstalling Windows can overwrite some, none, or all of the data. Creating a simple DBAN boot disk and using it mitigates all the risk.

As for the Windows licenses, if the license came bundled with the computer, or were bought individually, they can be given to someone else. You can always call Microsoft to confirm the validity of selling a license.

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  • The 7 pass may have been true, but in any case it would take an oscilloscope to read past the first one. Basically, it was a defense against a state-level power that essentially nobody needed ever. I don't think it's true of modern hardware.
    – Joshua
    Sep 22, 2018 at 3:51
  • 1
    The DBAN link is dead as far as I can tell, and I'm not sure it's maintained at all. There's a fork at github and it seems to be still on sourceforge. I'd prefer other methods myself. Sep 22, 2018 at 9:57
  • @StephenG DBAN link is working just fine... I actually just updated my USB key with DBAN on it.
    – Keltari
    Sep 22, 2018 at 10:16
  • @Joshua Ancient hard drives, up to about the early 1990s, needed multiple ovewrite passes for this reason. But it hasn't been necessary for decades. Sep 22, 2018 at 10:19
  • 2
    I'm getting a 504 error on dban.org everytime. Note that Wikipedia says DBAN is no longer worked on. Sep 22, 2018 at 11:49
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After Windows format and clean re installation of the OS overwrite all free space using the cypher command using the command prompt.

cipher /w:F

F would be the drive letter of the system volume which is usually C

Nothing can be recovered now, by anyone.

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2

To answer your initial question first; you are not safe by just reinstalling Windows, since you cannot guarantee that the data in question will be overwritten.

You may want to overwrite the (deleted) sensitive data using one of some available options;

You can use the DiskPart command - Clean All - but make sure that you know what disk you are working with.

You can (after deleting the sensitive data) use the Cipher command with the /W option.

You can also make yourself a simple BAT file or two - a couple of samples below;

One additional comment: If you wipe the disk/data 2-3 times, thereby alter the magnetic patterns beyond recognition, then even 'incredibly powerful people' will not be able to recover the data.

---

@echo off
rem Simple Disk Wipe Utility - wipedfast.bat
rem ---
rem --- 1) Delete all unwanted content from disk, leaving possibly only the command interpreter to run this script.
rem --- 2) Delete content from trashcan/recycled, if any.
rem --- 3) Run this script until it reports file system full.
rem --- 4) Delete WASH*.TMP files on each drive to reclaim space or to rerun utility.
rem --- Do this for all file systems/drives (C:, D:) on system, at least a couple of times.
rem ---
echo Grow file system test (fast / large increments - less secure). See comments in script file.
echo To be done for each drive (C:, D:) on system.
echo Abort with Ctrl-C when disk full and delete WASH-files
echo - Ideally run wipedfast.bat first - then wiped.bat when disk full - before deleting WASH-files.
pause
echo abcdefghijklmnopqrstuvwxyz0987654321ABCDEFGHIJKLMNOPQRSTUVWXYZ > wash_a.tmp

copy wash_a.tmp wash_b.tmp

:start
copy wash_a.tmp+wash_b.tmp wash_c.tmp
del wash_a.tmp
del wash_b.tmp
copy wash_c.tmp wash_a.tmp
ren wash_c.tmp wash_b.tmp
goto start

---

@echo off
rem Simple Disk Wipe Utility - wiped.bat
rem ---
rem --- 1) Delete all unwanted content from disk, leaving possibly only the command interpreter to run this script.
rem --- 2) Delete content from trashcan/recycled, if any.
rem --- 3) Run this script until it reports file system full.
rem --- 4) Delete WASH*.TMP files on each drive to reclaim space or to rerun utility.
rem --- Do this for all file systems/drives (C:, D:) on system, at least a couple of times.
rem ---
echo Wipe file system (slow / small increments - most secure). See comments in script file.
echo To be done for each drive (C:, D:) on system.
echo Abort with Ctrl-C when disk full and delete WASH-files.
echo - Ideally run wipedfast.bat first - then wiped.bat when disk full - before deleting WASH-files.
pause
echo abcdefghijklmnopqrstuvwxyz0987654321ABCDEFGHIJKLMNOPQRSTUVWXYZ > wash_a.tmp

copy wash_a.tmp wash_b.tmp

:start
copy wash_a.tmp+wash_b.tmp wash_c.tmp
del wash_b.tmp
ren wash_c.tmp wash_b.tmp
goto start
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0

Simply wiping the data (and overwriting it with random junk/zeroes) and installing a new windows is probably safe enough for you. At that point, any recovery of the old data will require the disk to be a HDD, physical access to the disk, really specialized forensic levels of knowledge, and important people caring a great deal about it.

If that's not safe enough, you need the fine powder method. I'd say it probably isn't, since we're talking cold war state secret levels of security.

If it's that important to you, you probably wouldn't post this question that'll save you a couple hundred bucks, because the security of this level doesn't care about money.

0

The one thing overlooked here, is the cheapness of hard drives.

If the data is truly sensitive, I have seen 2TB hard drives for $54-$65 online. You are likely to find cheaper 1tb hdd. If you want to sell them adding approx $60 for another hdd shouldn't be a barrier. Also the person purchasing it gets a new hard drive, possibly increasing it over all appeal.

https://www.newegg.com/Product/Product.aspx?Item=9SIA5AD3GM6130&ignorebbr=1&nm_mc=KNC-GoogleMKP-PC&cm_mmc=KNC-GoogleMKP-PC--pla--Hard+Drives-_-9SIA5AD3GM6130&gclid=CjwKCAjw0JfdBRACEiwAiDTALiOmQL0RDSIXjp3kbGMM9yceeukm6MxFn9SCWp7oVRIznlpCZ2NgHBoCk14QAvD_BwE&gclsrc=aw.ds

If each computer has a license key sticker, you can verify it from microsoft. Re-install windows with that key. If your company has a KMS server it has a different key.

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  • While this is an option, it isnt a good one, but not worth a downvote as it is somewhat valid 1) You are adding cost and complexity, when it is completely unnecessary. Simply wiping the drive is free and safe 2) He now has to do something with those drives. A) he has to destroy them , which costs time and money or B) he puts them in a secure place and monitors them, which requires time and money or C) reuse them. Both B and C eventually will bring us back to square 1 at some point.
    – Keltari
    Sep 23, 2018 at 6:22
  • @Keltari However, we don't know what his company requires. My companies insurance (data breach) requires all hard drives to be destroyed regardless of contents.
    – cybernard
    Sep 23, 2018 at 12:34

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