It is a common misconception that deleted files are completely removed from the hard drive, gone forever. However, highly sensitive data can still be retrieved from a hard drive even after the files have been deleted because the data is not really gone. Files that are moved to the recycle bin stay in that folder until the user empties the recycle bin. Yet even after they have been deleted from the recycle bin they are still located on the hard drive and can be retrieved with the right software.
Any time that a file is deleted from a hard drive, it is not erased. What is erased is the bit of information that points to the location of the file on the hard drive. The operating system uses these pointers to find every file on the hard drive. When the pointer is erased, the file essentially becomes invisible to the operating system. The file still exists; the operating system just doesn’t know how to find it.
It is, however, relatively easy to retrieve deleted files with the right software. The only way to completely erase a file with no trace is to overwrite the data. The operating system will eventually overwrite files that have no pointers so the longer an erased file remains in the hard drive the greater the probability that it has been overwritten.