Many people have some information that they would rather not share with others - passwords, private information, financial records, the list can be expanded much longer. probably you have stored some of this information on your computer where it is conveniently at your reach, but when the time comes to delete the information from your HDD, things get a bit more difficult and maintaining your privacy is not as easy as it may have seemed at a first glance.
Normal file deletion is insecure
Your first thought may be that when you erase a file, the information is gone. Unfortunately, when you erase file or folder, the Windows does not really remove the files from the hard disk; it only removes the reference of the file from the file system table. The information remains on the disk as long as another file overwrites it, and even after that, it might be possible to recover information by studying the magnetic fields on the disk platter surface. Before the file is overwritten, anyone can without difficulty view it with a disk maintenance or an undelete tool.
For instance, imagine that you have been browse the web for a while and afterwards want to clear all traces revealing what sites you visited. You go to Internet Explorer preferences and select to clear the cache and the history file, the information is now gone you think to yourself - well think again. The browser cache files can easily 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 properly overwritten before erasing. As simple as it looks, there are several difficulties in secure information erasing, mostly caused by the construction of a hard driver and the use of data encoding. These troubles have been taken into account when special eraser tool is designed and because this special design you can safely and easily delete private information from the hard disk.
You have probably already insecurely removed countless amount of files from your hard disk and from time to time programs create (and insecurely erase) temporary files on the hard driver containing some probably private data that you would rather not share with other people. This information remains on the HDD until it gets overwritten and can be viewed with simple hard disk software.
This is where the erasing of unused disk space can be useful. The erasing of unused hard disk space means that all space available on the hard disk will be overwritten so that files earlier saved on it cannot be restored. Good eraser software provides you a handy way to erase the unused hard disk space regularly in order to erase the all temporary files and other personal data you likely have had on your disk.
By now you must be asking what exactly this program does to my system when erasing data. You have come to the right place, the procedures gone through when erasing data are explained in this article.
After determining the type of the file (data compressed or encrypted at the file system level are supported on Windows NT and 2000, but Administrator privileges are required for low-level hard driver access), Eraser needs to determine the file size. When determining 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 method (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 hard disk and is not only cashed in a buffer somewhere. If the overwriting was successful, the last step is to correctly delete the file.
Before deleting the reference of the file from the file table (normal delete), the file will be truncated to 0 length to clear traces of the allocated clusters, the name of the file will be overwritten and finally file dates (creation/access/modified) will be scrambled to complete the data erasing.
Method of Gutmann
Based on Peter Gutmann's paper "Secure Deletion of Data from Magnetic and Solid-State Memory", this method provides the best security. File will be overwritten 35 times with carefully selected patterns, which makes it unrecoverable.
The 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 written 7 times making this method significantly faster than the Gutmann's Method, 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 recommended method that should be used when removing unused space or files on a compressed drive. The number of passes is user selectable from 1 to 65535.
Being the fastest method, this one is used as default for erasing free hard disk space.
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