Data remanence is the residual representation of data that have been in some way nominally erased or removed. This residue may be due to data being left intact by a nominal delete operation, or through physical properties of the storage medium. Data remanence may make inadvertent disclosure of sensitive information possible, should the storage media be released into an uncontrolled environment.
A common method used to counter data remanence is to overwrite the storage medium with new data. This is often called wiping or shredding of a file or disk. Because such methods can often be implemented in software alone, and may be able to selectively target only part of a medium, it is a popular, low-cost option for some applications. Overwriting is generally an acceptable method of clearing, as long as the media is writable and not damaged.
Some file eraser software make use of a simple overwrite technique, which writes the same data everywhere, often just a pattern of all zeros. At a minimum, this will prevent the data from being retrieved simply by reading from the medium again using standard system functions.
To counter more advanced data recovery techniques, specific overwrite patterns are often prescribed. These may be generic patterns intended to eradicate any trace signatures. For example, writing repeated, alternating patterns of ones and zeros may be more effective than zeros alone. Combinations of patterns are frequently specified. REMO Shredder is a powerful file eraser software, which provides nine different shredding methods, that exceed standards prescribed by various government and law enforcement agencies around the world.