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Data is stored on a hard disk as a sequence of 1s and 0s (ones and zeros) represented by differently magnetized parts of a disk. Information removed from a hard disk drive by non-secure means (for example, by simply deleting the file) can easily be recovered by file recovery software. By using specialised equipment, someone may be able to recover even repeatedly overwritten information.
When you delete a file from your disk, Windows deletes the reference to that file from its File Allocation Table (FAT), but the actual data remains on your hard disk in the same sectors in which it previously existed. Even deleting partitions or formatting your hard drive wont actually remove the data. It remains for prying eyes to see whether its financial information (such as online banking information, payroll data, social security numbers or credit card numbers), confidential e-mail messages, personal photos or other private information. If you leave critical data on the disk, a knowledgeable person can look into your private information and crime, such as identity theft, becomes easy.
To prevent data retrieval, the existing data must be destroyed. You permanently destroy data by writing over it usually with some pattern (such as all zeroes, 00000, or all ones, 11111). Sophisticated data thieves can read or interpret deleted data and can retrieve that information even from reformatted drives. Therefore most standards implement permanent destruction by repeatedly writing patterns over the original data. |