A lot of people have some files that they would rather not share with anyone - passwords, sensitive data, self-written poems, the list can be expanded much longer. probably you have saved some of this information on your computer where it is easily at your reach, but when the time comes to remove the data from your hard disk, things get a little bit more complicated and maintaining your privacy is not as simple as it may have seemed at a first glance.
Standard file removal is insecure
Your first thought may be that when you erase file or folder, the data is gone. Unfortunately, when you delete file or folder, the operating system does not really remove the files from the HDD; it only removes the reference of the file from the file system table. The information remains on the hard disk as long as another file is created over it, and even after that, it might be possible to recover data by exploring the magnetic fields on the disk platter surface. Before the file is overwritten, anyone can without difficulty get it with a disk maintenance or an undelete utility.
For example, imagine that you have been surfing on the web for a while and then wish to remove all traces revealing what sites you read. You go to Internet Explorer preferences and select to clear the cache and the history file, the data is now gone you think to yourself - well think again. The browser cache files can without problems be restored with an undelete utility and your privacy is once again compromised.
To be sure that a file is gone, it 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 data encoding. These difficulties have been taken into account when special eraser software is designed and because this special design you can safely and without difficulty delete private data from your disk.
You have probably already insecurely erased large amount of files from your hard disk and from time to time applications create (and insecurely remove) temporary files on the disk containing some possibly sensitive information that you would rather not show to other people. This data remains on your hard driver until it gets overwritten and can be restored with simple HDD utility.
This is where the erasing of unused hard disk space comes in handy. The erasing of unused HDD space means that all free space on the disk will be overwritten so that files previously stored on it cannot be retrieved. Good eraser tool provides you a convenient way to erase the free hard driver space regularly in order to delete the all temporary files and other personal information you likely have had on your HDD.
By now you must be wondering what this program does to my PC when erasing data. You have come to the right place, the procedures gone through when erasing files are explained here.
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 HDD access), Eraser needs to determine 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.
After the size is calculated, the data will be overwritten with the special technique (see detailed 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 cashed in a buffer somewhere. If the overwriting was done, the final step is to correctly erase the file.
Before removing the reference of the file from the file table (normal delete), 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, modified) will be scrambled to complete the data erasing.
Method of Gutmann
Based on Gutmann's article "Secure Deletion of Data from Magnetic and Solid-State Memory", this method provides the best security. Data will be written 35 times with carefully chosen patterns, which makes it unrecoverable.
This method is used as the default for deleting files, but has been proven to be very slow when erasing free space on a hard disk (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 Gutmann's Method, but also less secure when it comes to hardware recovery.
Pseudorandom Data
All passes will be random data, which is very incompressible. Therefore, this is the only method that should be used when removing unused space or files 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 removing free HDD space.
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