Secure erase a.k.a. data wiping
If you need to delete a file irreversibly, it is not enough to just delete it and then empty the Recycle Bin. Data recovery software is quite capable of restoring data that was deleted in such a way. In earlier days, when the FAT filesystem was widely used, it was sufficient to write some garbage data to the file. To overwrite the file data completely, the garbage data size should be no less than the original file size. This worked because FAT is rather simple filesystem. With the filesystem complexity increasing, a number of filesystem features which should be taken into account is increased as well. Nowadays, it is no longer enough just to write other content to the file to delete it irreversibly. For example, if a file is stored on the NTFS filesystem in compressed form, then depending on the compressibility of the data in the original file (to be secure erased) and a new content, most likely a new set of clusters would be allocated for the new file data. Therefore, the original f...