Deleting is more complicated than it sounds. Moving a file to the Recycle Bin and then emptying the Bin doesn't really delete the file from the hard disk. The directory entry is removed, but the data itself remains on the hard disk and can therefore be restored. Formatting a partition is also not usually enough. Even a low level-formatting on the BIOS level is no secure solution, since data - even if it requires more effort - can always be reconstructed.