A lot of people have some information that they would rather not share with anyone - passwords, sensitive information, classified documents from work, the list can be expanded forever. Perhaps you have saved some of this data on your computer where it is conveniently at your reach, but when the time comes to erase the files from your HDD, things get a bit more complicated and saving your privacy is not as easy as it may have seemed at first.
Standard file and folder erasing can be insecure.
Your first thought may be that when you delete a file, the data is gone. Unfortunately, when you erase file or folder, the OS does not really remove the files from the HDD; it only removes the reference of the file from the file system table. The data keeps on the hard driver as long as another file is created over it, and even after that, it might be possible to recover information by exploring the magnetic fields on the disk platter surface. Before the file is overwritten, anyone can easily get it with a disk maintenance or an undelete utility.
For instance, imagine that you have been surfing on the Internet for a while and afterwards wish to clear any traces revealing what pages you visited. You go to Internet Explorer settings and select to delete the cache and the history file, the information is now gone you think to yourself - well think again. The browser cache files can with no trouble be restored with an undelete software and your privacy is once again compromised.
To be sure that a file is gone, its contents must be appropriately overwritten before deleting. As simple as it looks, there are several difficulties in secure data erasing, mostly caused by the construction of a disk and the use of files encoding. These troubles have been taken into account when special eraser utility is designed and because this intuitive design you able to safely and easily delete sensitive files from your hard disk.
You have most likely already insecurely erased countless amount of files from the hard driver and from time to time applications create (and insecurely remove) temporary files on your HDD containing some possibly personal data that you would rather not show to anyone. This data remains on the disk until it gets overwritten and can be restored with simple HDD utility.
This is where the erasing of unused hard driver space can be useful. The erasing of free hard driver space means that all unused space on your HDD will be overwritten so that data earlier saved on it cannot be retrieved. Good eraser software provides you a convenient way to erase the unused hard driver space regularly in order to remove the remains of temporary files and other sensitive data you possibly have had on your hard driver.
You must be asking what this application does to my computer when erasing data. You have come to the right place, the procedures gone through when erasing files are explained in this article.
After determining the type of the file (data encrypted or compressed at the file system level are supported on Windows NT and 2000, but Administrator rights are required for low-level HDD access), Eraser needs to calculate the size of the file. When calculating the size, the cluster tip area is included so the data stored on it will be erased too.
Once the size is calculated, the data will be overwritten with the special technique (see full descriptions of the techniques bellow). Eraser tool takes care of flushing write buffers to make sure that the data really gets written to the disk and is not only saved in a buffer somewhere. If the overwriting was successful, the final step is to correctly erase the file.
Before deleting the reference of the data from the file system (normal remove), the file will be truncated to zero length to clear traces of the allocated clusters, the filename will be overwritten and finally file dates (creation, access and modified) will be scrambled to complete the file deleting.
Gutmann’s Method
Based on Gutmann’s article “Secure Deletion of Data from Magnetic and Solid-State Memory”, this method provides the best security. File will be written 35 times with carefully selected patterns, which makes it unrecoverable.
This method is used as the default for erasing data, but has been proven to be very slow when clearing free space on a hard driver (could be several gigabytes).
A Faster Method - US DoD 5220-22.M
Two methods based on United States Department of Defense recommendation 5220-22.M from January 1995. The data will be overwritten seven times making this method much faster than the first one, but also less secure when it comes to hardware recovery.
Random Data
All passes will be pseudorandom data, which is very incompressible. Therefore, this is the only method that should be used when deleting free space or information on a compressed drive. The number of passes is user selectable from one to 65535.
Being the fastest method, this one is used as recommended for deleting unused disk space.
By: Jim.Olivera, open source file deleting program
April 27th, 2009 by admin | No Comments »