Wednesday, Jan 22 2014 06:00 AM

Tech Wire: How to securely erase your data

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Matthew Sgherzi

When you don't want a file or folder any longer on your computer or smart device, you highlight it and hit "Delete." You are careful, so you also erase the Recycle Bin (or equivalent). After that, it's gone forever... right?

What really happens when you hit 'Delete'

A hard drive, USB device or any other storage medium (even your smart device) uses a File Allocation Table. Deleting a file simply removes the entry from that table, but the file actually remains for quite some time. It is not difficult for someone with some simple software to recover anything from deleted files to web history with very little effort. So, while having the ability to delete your files allows you to remove them from your immediate view, it does not permanently remove them from your hard drive. All this does is give you the "sense" that they're gone and allow you to free up space as well as not have to see or deal with those deleted objects again.

How data "should" be removed

There are ways, like everything else, of securely removing your data beyond recovery. Fortunately, these ways are becoming easier and easier. With free software becoming popular and containing a rich amount of options, securely erasing your data can be done with just a few clicks, in most cases. It becomes important to understand "how" exactly this process works.

In order to remove files or any other data beyond recovery, every literal "bit" of the file must be overwritten with useless "junk" data. Because every "wipe" of every "bit" contains randomized junk data in randomized patterns, it is impossible to reverse engineer or decrypt, since neither can be predicted. When the U.S Government wants to securely remove data, they perform three wipes on each file, the Canadian Police use five and the NSA uses seven. However, in 1996, Peter Gutmann wrote a very famous paper entitled Secure Deletion of Data from Magnetic and Solid-State Memory. In this paper, Gutmann supplies a series of mathematical formulas and principles for secure deletion of data.

In this paper, Gutmann recommended the highest and most secure way of deleting data by overwriting each bit of every file not three, five or seven times, but thirty-five times. To date, security experts from the NSA have only successfully recovered a file after it has been overwritten only five times.


Because this has become the gold standard method for securely removing data off a storage medium, there are a lot of software options available that can perform these methods (and more). The most popular computer cleaning software and one I recommend is "CCleaner" by Piriform. In the options, you can set it to use the Gutmann method on each file you decide to erase including your own personal files, web history, cookies and other tracks that almost all programs leave behind.

However, if you're looking to erase an entire hard drive, which is particularly useful for when you're looking to give, sell, loan or even donate your computer, I recommend a program called "Darik's Boot and Nuke", or DBAN for short. You will need to download DBAN, burn it to a CD or DVD, boot from that CD or DVD, then run the program with the specified options you desire. Keep in mind: The larger your hard drive or device is and the more data you have on it will both be factors in how long this will take. It is not uncommon for entire drives to take weeks to be overwritten using Gutmann or any higher end security method.

Solid State Drives

Bear in mind that, as of right now, the methods described above do not work the same if your computer is using a solid state hard drive. The newest solid state hard drives cannot have files overwritten in the same manner. Any time you delete a file in general, the longer you wait, the more difficult it becomes to recover, and that may be the only thing right now that can come close to securely removing files off a solid state drive. Since an exact method of securely removing files off a solid state drive is still murky right now, it is best to encrypt the drive for the time being using software such as True Crypt or Windows' built-in Bit Locker feature until the American National Standards Institute can negotiate a series of definitive methods.

MATTHEW SGHERZI lives in Tehachapi where he has operated an IT business since 2007 (tehachapicomputers.com).

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