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I have an external hard disk and a HDD that was formally internal but is now connected via a SATA-to-USB adapter.

I'd like to wipe both drives, but I feel uncomfortable booting into DBAN and other similar software because I don't want to accidentally wipe any of my internal drives.

I'm considering deleting all root folders in both drives by opening Windows Explorer, going into I:\ and J:\, highlighting all the folders, and then Alt-Del. After that I would execute ccleaners 'Wipe Free Space'. However, I don't know how effective that is (is it really erasing everything including system directories and recycle bins?).

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Nitpick: there's only one root folder on each partition, namely X:\ (for a given X). What you see there is subfolders to the root folder. (Or directory...) –  Michael Kjörling Sep 21 '13 at 20:02
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You mean Shift+Del instead of Alt+Del, do you? –  Alvin Wong Sep 22 '13 at 7:03
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5 Answers

up vote 5 down vote accepted

It sounds like you want a 'secure erase' or a zero pass to be done, is that correct?

From format /?:

/P:count        Zero every sector on the volume.  After that, the volume
                will be overwritten "count" times using a different
                random number each time.  If "count" is zero, no additional
                overwrites are made after zeroing every sector.  This switch
                is ignored when /Q is specified.

format J: /P:0 and format I: /P:0 should do the trick for you. Make sure you open the command prompt as administrator.

If you're not looking for a secure erase, and just want to make sure everything on the drive is erased for your personal use later, use the commands format J: /Q and format I: /Q, this will do a quick format and be (obviously) much faster than running a zero pass on the drive.

Alternatively, you can do a quick format from a GUI by right-clicking the drive and selecting the Format option.

Deleting files by hand will be messy a slow. I would avoid it. I'm also not particularly a fan of anything related to CCleaner. Windows has its own simple, built in methods to erase a disk.

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My bad, I didn't specify that I'm only interested in secure options ( I want to sell the drives). Why do you recommend count=0? Isn't more safer? –  Wuschelbeutel Kartoffelhuhn Sep 22 '13 at 0:59
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One pass is enough realistically. Take a look at this question and this article. If you're that worried about the data, you should be physically destroying the disk instead of selling it. Though I will admit I run a couple passes myself, just out of paranoia. :) If you have the patience and it will make you sleep better at night, go for it. –  Tanner Sep 22 '13 at 1:58
    
I am selecting this answer because it is the simplest (does not require any third party software and can be run while I can do other tasks) and makes the data virtually unrecoverable. Thanks for all the other great answers though. –  Wuschelbeutel Kartoffelhuhn Sep 22 '13 at 15:24
    
If drive has multiple partitions use FORMAT /P for each partition (or delete all but one first) (not in original post?). /P is only available in Vista or later (7 in OP). Won't work on primary (OS) partition (not in OP). Detailed instructions for creating a system repair disk (or using Vista or later install disk) that will work on any Windows primary partition as well as any XP partition: pcsupport.about.com/od/toolsofthetrade/ht/… (I found this while looking for evaluation of FORMAT /P. I haven't reviewed HELP FORMAT in years.) –  BillR Oct 8 '13 at 19:49
    
FORMAT is run in Command Prompt (as an admin). For a GUI approach (possibly preferable to Wuschelbeutel Kartoffelhuhn), use Disk Management instead. DM also allows combining all partitions on a drive first -- or at least reminds you there may be more than one (including hidden ones). Select Format from the context menu. Do not check Quick Format on the format popup. Per MS: "By default in Windows Vista, the format command writes zeros to the whole disk when a full format is performed." Since a format is either quick or not, .... support.microsoft.com/kb/941961/en-us –  BillR Oct 8 '13 at 20:33
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If you are that concerned about picking your internal hard disks by accident, you can always disconnect them by removing the SATA cables. By doing this, they will not show up when you boot DBAN.

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Thats a nice (and obvious) solution I didnt think of. However, I'm not sure if DBAN has the necessary drivers to recognize external USB drives. –  Wuschelbeutel Kartoffelhuhn Sep 22 '13 at 1:28
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Usually DBAN does actually. I've used it on stubborn USB drives plenty of times. –  Tanner Sep 22 '13 at 2:04
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This is exactly how I do it. Disconnect internal drives and boot from cd. Remember to unplug any other usb drives you have as well. DBAN has detected every usb drive I have tried. –  Grant Sep 22 '13 at 3:21
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You can use FileShredder found here: http://www.fileshredder.org/ format the drive(s) first, then use the feature called "shredder free space"... or use this one (faster): http://www.mediafire.com/download/1pmghofp64hdqrz/DiskNuke.zip (One pass wipe is more than sufficient for todays drives...)

Answer to your question: Filesystems divides the space in your harddrive into unit sizes, usually between 4KB and 64KB, then keeps track of all the units in a database. When you delete a file from the recycle bin, the filesystem marks the space as "free", but the data is still there and can be recovered by data recovery software. When new data is written to the drive, old data will eventually be overwritten by the new data. Disk wiping programs will fill your drive(s) up to several times with random data that will erase all deleted files, and make it close to impossible to recover them.

The security of a disk wiping mode is generally messured in the amount of passes that it preformes, that is, how many times does it overwrite the data. This can be anything between single pass(1 time) to gutmann 35 passes and upwards...

On older drives it is/was common to use multiple passes in the hope of eliminating shadow data (traces of the magnetical state of the next or previous bit) which could sometimes be found using electron microscopy. However, the bit density of current drives makes shadow data extremly unlikely and anything more than a single pass wipe is considered overkill.

Disk wiping is about as secure as you can get without destroying the drive physically.

As for the hidden files and directories, formatting the drives first will get rid of them...

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I don't have CCleaner, but according to the docs, the current version at least has an option to wipe an entire drive. It even does not allow wiping the boot drive as a safety feature.

If that doesn't work for some reason, a fallback would be to format the entire drive, so that it is practically empty, and then wipe all the free space. You would choose the FAT format, since that is the simplest and has the least overhead comprising directories, cluster maps, etc. Depending on those areas are initialized, there might be some remnants of data that is not overwritten, but the exposure is minimal.

To your original question, files deleted from system directories are considered part of free space, since they are no longer "held" by a directory. Files in the Recycle Bin are not, since the Recycle Bin is actually just a special directory. (Although a cleaner program might specifically wipe the Recycle Bin as part of a "clean" operation.)

Hidden directories are also a more general problem with using Windows Explorer, since highlighting and deleting all the folders from there with Shift-Del will not delete those hidden folders.

There are other alternatives for wiping disks, but the easiest ones -- like using dd on Linux or Mac -- require typing a drive specifier; the difference between your boot disk and other disk is typing something like "hd2" and not "hd1", so that is also easy to get wrong.

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Per your question, we are not talking about erasing the OS drive(s) that are currently in use.

Keep in mind that the tool required depends upon the drive because different types of drives use different storage technologies: hard disk drive v. SSD v. USB flash v. hybrid. I assume you are referring to standard hard drives.

If the drive itself is compressed or encrypted (e.g., NTFS option), the rules are different. Individual zip files or files compressed or encrypted by 7-Zip, AxCrypt or the like are just data files with weird data but compressed or encrypted disks behave differently (see SDelete discussion referenced below).

If you go the CCleaner route, remember to clear the recycle bin! Also the filenames will not be securely deleted (but data "should" be) and there may be some miscellaneous file fragments left. If the drive itself is compressed or encrypted, I'm not sure that CCleaner will do what you want.

SUGGESTION: Check the vendor website for each of your disks. Some disks can be 100% securely erased in 1 second by overwriting an internal encryption key.

SUGGESTION: Try SDelete from Sysinternals (now part of Microsoft). It is a free program that can be used to wipe drives, wipe files, or wipe free space. The background material is quite informative and will help you evaluate various suggestions. Note that this is not guaranteed to make all old filenames completely unrecoverable but it should come pretty close. File contents will be overwritten.

http://technet.microsoft.com/en-us/sysinternals/bb897443 or search for sysinternals sdelete

The following is adapted from http://gizmodo.com/5489933/leave-no-trace-how-to-completely-erase-your-hard-drives-ssds-and-thumb-drives which also has good background information and suggestions.


Download SDelete.zip from technet.

Unzip (extract) to a folder.

Copy sdelete.exe to c:\windows\system32\ (or the appropriate directory for your OS) so you can run it from anywhere.

Open a command prompt session with Administrator rights (press START button; enter CMD in the start search field; right click on CMD.exe and choose Run as Administrator).

To wipe all files on drive X: and its subdirectories and to wipe free space, enter two lines:

ECHO ON

Sdelete -a –s -z X:*.*

BE VERY CAREFUL about the drive letter!!!

Wait: this could take minutes to hours. You'll see status messages unless you use ECHO OFF command.


I used SDelete a few years ago so please report back if you encounter a problem with these instructions or can clarify them.

If you really want to be sure, perform 2 cleaning passes. Anything more than that is not relevant to the technology in multi-GB drives. Sdelete -a -p 2 –s -c X:*.*


Usage: sdelete [-p passes] [-s] [-q] ... sdelete [-p passes] [-z|-c] [drive letter] ... -a Remove Read-Only attribute. -c Clean free space. -p Passes Specifies number of overwrite passes (default is 1). -q Don't print errors (Quiet). -s or -r Recurse subdirectories. -z Zero free space (good for virtual disk optimization).

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