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How to delete a set of files permanently beyond most reasonable means of recovery .

Posted on 2016-10-06
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Last Modified: 2016-10-06
I know that the ultimate way is physical destruction of the media .
However I am faced with a situation where i need to absolutely guarantee that some picture which exist on an IMAC are deleted and cannot be recovered . I need a utility . I need a method short of nuking the computer .
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Question by:Andre P
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Dr. Klahn earned 500 total points
ID: 41832384
There are numerous utilities available doing this.  Here's a link to a page reviewing some of them.
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by:Wayne Herbert
ID: 41832402
Secure Erase is a method that uses built in commands on PATA and SATA drives.  The whole drive is erased and will be extremely unreadable.
 
Information about Secure Erase:  http://pcsupport.about.com/od/termss/g/secure-erase.htm

I used this $9 purchased Secure Erase:  https://partedmagic.com/downloads/

https://partedmagic.com/secure-erase/

There are other freebies available:  http://pcsupport.about.com/od/toolsofthetrade/tp/free-data-destruction-software.htm  Look for the ones that use Secure Erase as the sanitizing option.

I use this erase program when none of the others will work... works on HDD, no reports:  http://www.dban.org/
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Expert Comment

by:Gary Patterson
ID: 41832423
No such thing as "absolutely guarantee".  Systems are too complex, and data gets copied around under the covers all the time: swapfiles used for virtual memory, applications that make copies of files while using them and then delete them insecurely, SSD and disk blocks that get marked bad but still contain recoverable data.

If it is really important, you need to securely erase the entire disk(s), and reload from scratch or from a backup from before the problem file entered the system.  A determined data recovery pro may be able to turn up very interesting bits of information even if you take all the actions I describe below.

To permanently delete files on some older versions of Mac OSX:

    Place Moderate or High Risk Data you wish to permanently remove in the Trash.
    From the Finder menu, select Secure Empty Trash…  
    Items in the Trash are to permanently erased to US DoD standards.

Newer versions of OSx don't have this feature, but you can use the srm command instead:

https://developer.apple.com/legacy/library/documentation/Darwin/Reference/ManPages/man1/srm.1.html

Even securely deleting a file -does not ensure- that all evidence of a file is truly removed from a system.

https://ssd.eff.org/en/module/how-delete-your-data-securely-mac-os-x

Delete cache, log and temp files:

http://www.chriswrites.com/cleaning-up-cache-log-files-and-temporary-files-in-os-x/

Finally, disable virtual memory, delete swapfiles, securely wipe free space, reboot, and re-enable virtual memory.  

http://hints.macworld.com/article.php?story=20040809191855264

Finally, I am an IT security guy, but Mac OS is not my specialty, so I may have left out some important steps.  Proceed with caution, and if in doubt, securely wipe the magnetic drives in question, replace SSD drives with new ones and physically destroy the old ones, and be careful about copies that might have gotten stored elsewhere: mail server, web site, cloud storage, backup devices, etc.
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Expert Comment

by:Wayne Herbert
ID: 41832439
You may also wish to read the articles at this website concerning the various techniques for a secure erase and how long they take.  http://cmrr.ucsd.edu/people/Hughes/secure-erase.html

http://cmrr.ucsd.edu/people/Hughes/documents/DataSanitizationTutorial.pdf

Interestingly enough, DOD 5220 is not very good.  Using the drive's built in features is both much faster and much better.
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