Data Removal Recommendations

1.0 Overview
2.0 Sanitizing Techniques
3.0 Suggested Software
4.0 Removal Tips
4.1 Windows
4.2 Macintosh
4.3 Unix / Linux / Solaris
5.0 Related Links

1.0 Overview

For the general user, the delete or format command appears to be the logical method of removing unwanted data files. These methods, however, are like sweeping something under the carpet: you may not be able to see it, but it's still there. All that deletion has done is remove the pointer to the files, with the data itself residing in unallocated space on the hard drive. This means that data recovery is possible using various software tools.

When sensitive information is stored on the hard drive of a machine that is to be surplussed or transferred to another individual or department, it is therefore imperative that extra measures be taken to wipe clean the hard drive before the computer leaves your area of responsibility. This document describes some common methods and software to assist you with the sanitization process. It also includes links to articles that provide detailed technical descriptions of what occurs during this process.

2.0 Sanitizing Techniques

As described in the much-referenced article Remembrance of Data Passed: A Study of Disk Sanitization Practices, the three most common techniques for properly sanitizing hard drives are:

  1. Physically destroying the drive, rendering it unusable. This is a good alternative for defective hard drives or those that would be too costly to repair. For added security, the disk should be overwritten or degaussed prior to destruction.
    N.B. Hard drives, cell phones, and PDAs that are no longer needed and contain data covered under the Brown Restricted Information Policy can be brought to the offices of ISG for crushing and disposal. Please contact ISG to schedule an appointment.
  2. Degaussing the drive to randomize the magnetic domains – most likely rendering the drive unusable in the process. Degaussing, or demagnetizing, applies a reverse magnetizing field to data stored on magnetic media, erasing the contents by returning the magnetic flux to a zero state.
  3. Overwriting the drive's data so that it cannot be recovered. Overwriting replaces previously stored data on a drive or disk with a predetermined pattern of meaningless information, rendering the data unrecoverable.

The SANS white paper "Deleting Sensitive Information: Why hitting delete isn't enough"1 explains: "...Overwriting data once is not usually good enough to prevent data recovery, instead it is recommended that a minimum of three passes are made writing alternating zero and one patterns over the data and then further passes with random data, the more passes the better the chance that no data can ever be recovered."

Note that when removing sensitive information, don't forget storage devices such as thumbdrives, back-up external hard drives and CDs. Also, be sure to erase any stored names and numbers from phones and fax machines.

EXTRA: CIS has a hard drive crusher used for crushing no-longer needed drives containing data covered under the Brown Restricted Information Policy. Contact the IT Service Center for more details and to arrange an appointment.

3.0 Suggested Software

The following chart is a collection of disk wiping software recommended by departmental computing coordinators (DCCs) or listed on a variety of other University and security sites. The inclusion of any title does not indicate an endorsement by Brown University or the CIS department, and has only been provided as an aide in making a decision that best matches your specific needs. See also the Wikipedia list of data-erasing software.

Program Cost Platform Comments
Darik's Boot and Nuke (DBAN)
 		 Shareware Windows & Mac Self-contained boot disk that securely wipes the hard disks of most computers; consumer-grade, appropriate for bulk or emergency data destruction. (Acquired by Blancco in 2012.)
Disk Utility Free Mac OS X Securely erases data as well as disk’s empty space (latter prevents the recovery of erased files without erasing the entire disk).
Disk Wipe Shareware Windows Permanently wipes sensitive data on partitions and disk volumes.
East-Tec DisposeSecure $29.95 OS independent Erase computer hard drives, partitions or media devices; US DOD compliant.
Eraser Shareware Windows Completely removes sensitive data from a hard drive by overwriting it several times with carefully selected patterns.
KillDisk (Active@KillDisk) Free version, Pro versions start at $39.95 Windows, Linux Powerful and compact software allowing you to destroy all data on hard disks, SSD and USB drives completely, excluding any possibility of future recovery of deleted files and folders; a hard drive and partition eraser utility.
Linux Free Linux Use built-in dd, wipe and shred tools
Paragon Disk Wiper Professional
 		 $39.95 Windows Disk Wiper Pro meets DoD sanitizing standards; includes 10 different disk sanitization methods
sDelete Free Windows

A command line utility that allows you to delete one or more files and/or directories, or to cleanse the free space on a logical disk; DoD-compliant secure delete program.
secure rm Shareware Unix & Windows command line program Secure file removal utility for Unix and Unix-like computer systems; command-line compatible rm overwrites file contents
ShredIt Free trial, $24.95 Windows, Mac, iOS, Android Easy interface, configurable overwrite pattern and number of overwrites
Wipe Shareware Linux, Unix Uses Gutmann's erase patterns, erasing single files and accompanying metadata or entire disks
WipeDrive (Home version) $29.95 Windows, Intel-based Macs, Linux Securely erases all hard drive or external storage information; military grade; wipe up to 3 different hard drives
WipeDrive (Enterprise version) Contact vendor for details (licensed per client) Windows, Intel-based Macs, Linux Flexible licensing permits wiping desktops, laptops, networked computers, servers, individual drives, or RAID arrays with one product and one block of licenses. Erase hard drives remotely.

4.0 Removal Tips

4.1 Windows

Each of the software products listed above comes with specific instructions, some with an easy-to-use wizard interface. KillDisk (recommended by some DCCs) is the software of choice at Northern Illinois University. Their support for this product includes detailed instructions on its use. Dell offers an overview document How Do I Erase Data from My Hard Drive?.

4.2 Macintosh

In addition to the software offered above, Mac computer hard drives can be cleared by zeroing their data. Note that zeroing data (aka "low level" format) may take a long time and depends on the hard disk size. It is recommended to use the "8-way random" feature in conjunction with the "zero all data" option.  See the section "Securely erase a disk" in the article Disk Utility 12.x: Erase a Disk, CD or DVD for details.

    4.3 Solaris / Linux / Unix

    5.0 Related Links

    Compendium of disk wiping software:
    Further Reading:
    Related sites at other universities:

    Last Reviewed: March, 2016
    Next Scheduled Review: March, 2018