Information Security Tips Series
Are you aware your data may still be inside the hard disks even if you have "deleted" them? Many recent incidents have showed disposed hard disks are treasures for "interested parties" as data could still be retrieved from the "deleted" files or "free space" inside these hard disks. Although many people are aware of data security and "delete" all data or "format" hard disks before disposal, these methods only remove the "index" or "pointer" of the files but the actual files or data may still remain untouched in hard disks. These methods are not secure enough.
Secure erasure is one of the ways to prevent any "deleted"data from being retrieved from hard disks. In general, there are three methods, (1) overwriting, (2) degaussing and (3) physical destruction. Three methods have pros and cons.
Secure erasure software, whether paid or free, makes use of overwriting technique to erase the actual data areas of the files in hard disks. Once overwritten, the files or their content can no longer be retrieved easily. Depending on the security level required, different overwriting techniques or standards, like one-pass overwriting and US DoD method, use different overwriting passes and various data patterns. Although overwriting is cost effective and powerful, it is time-consuming. It is not always a perfect solution if hard disks contain bad sectors or malfunction. Bad sectors or malfunctioning may make the data areas inaccessible or unable to be overwritten by software.
Degaussing and physical destruction
Degaussing uses strong and changing magnetic fields to destroy the magnetic patterns and hence the data in hard disks. Physical destruction means breaking a hard disk into pieces. Both can overcome the problems of bad sectors or malfunctioning of a hard disk. Nevertheless, they have drawbacks. Firstly, degaussing and physical destruction can be used on a whole hard disk only but not individual file or partition. Secondly, hard disk cannot be re-used or functional afterwards. Lastly, these methods require proprietary equipment that is expensive for general users. Users can only approach service providers for erasure service.
The above methods may not be used in other hard disks like Solid-State Drives (SSD) or USB thumb drives. Owing to the different ways storing data and data management algorithm from traditional magnetic hard disks, some advanced storage devices like SSD and USB thumb drives may make certain overwriting techniques ineffective. Degaussing cannot erase the data of such drives.
On one hand, secure erasure prevents data from being retrieved by others, and on the other hand, you cannot rescue any files that have been deleted accidentally. Disposal of storage device is not an easy task in the modern IT world and new storage technologies are also bringing new challenges of secure erasure. Users should make sure the method chosen is compatible and can erase the data in such hard disk or storage device.
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