Software based data destruction involves using a special application to write patterns of meaningless data onto each of the hard drive’s sectors. This process works by overwriting the data with a combination of 1’s and 0’s. The level of security depends on the number of times the entire hard drive is written over. The Department of Defense requires 3 levels of overwriting. There are many data erasure software program however not all offer complete security. Disk overwriting tools that are unable to access the entire hard disk which include hidden/locked areas such as Host protected area (HPA), device configuration overlay (DCO), remapped sectors, perform an incomplete erasure, leaving some of the data intact. In order to eliminate the risk of incomplete erasure, an overwriting tool must be able to access all areas on the hard drive. A secure data erasure tool should also be able to bypass the BIOS and OS. Software tools that operate through the BIOS and OS will not always perform a complete erasure due to altered or corrupted BIOS data and may report back a complete and successful erasure even if it wasn’t able to access the entire hard disk. This leads organizations to believe that all of the data has been completely destroyed, hence providing a false sense of security.

According to a memorandum issued by the United States Department of Defense (DoD), (2001, May), overwriting software must have the following functions and capabilities in order to ensure the integrity of the sanitization process:

• The ability to purge all data or information, including the operating system (OS), from the physical or virtual drives, thereby making it impossible to recover any meaningful data by keyboard or laboratory attack.
• A compatibility with, or capability to run independent of, the OS loaded on the drive.
• A compatibility with, or capability to run independent of, the type of hard drive being sanitized (e.g., Advanced Technology Attachment (ATA)/Integrated Drive Electronics (IDE) or Small Computer System Interface (SCSI) type hard drives).
• A capability to overwrite the entire hard disk drive independent of any Basic Input/Output System (BIOS) or firmware capacity limitation that the system may have.
• A capability to overwrite using a minimum of three cycles (six passes) of data patterns on all sectors, blocks, and slack or unused disk space on the entire hard disk medium.
• A method to verify that all data has been removed from the entire hard drive and to view the overwrite pattern

Although not mandatory, selected software should also:

• Provide the user with a validation certificate indicating that the overwriting procedure was completed properly.
• Provide a defects log list, or listing of any bad sectors, that could not be overwritten by the software.

Advantages

• An effective and convenient way of permanently destroying data
• The erased media can be reused
• Increases the remarketing value of the IT asset
• Can be deployed over the network to target specific PCs. Erasure reports can be sent to a central database offering centralized management.
• Software tools that provide detailed reporting of the erasure process are able to validate the erasure of the media. Reports contain data such as:
  o Hard drive serial number
  o Information on the PC erased
  o Date of erasure
  o Name of technician
  o Results/errors concerning the erasure process
  
• Can be performed in-house eliminating the risk of media being stolen during storage or transit to a third party

Disadvantages

• Cannot be used if the media is damaged or is not writeable.
• Not all overwriting tools are able to erase data on the locked/hidden sectors thus compromising data security.
• Most overwriting tools operate through the BIOS which results in an incomplete erasure being performed as the BIOS provides inaccurate information on the size of the hard disk
• Most overwriting tools do not provide detailed reporting of the erasure process therefore providing no audit trail
• Many freeware/shareware tools exist which perform an incomplete erasure putting a company at risk of a data breach.

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