It is true this is how some of these information retrieval programs work in case of accidently deleting the wrong thing. The data you delete is still on the hard drive until the area on the hard disk it is on is written over by another program.
It's far more difficult to delete than is often realised and even after overwriting it is possible sometimes to still read what is on teh disk. There is software available (not to the public) that can see all sorts of things ostensibly deleted from hard drives. Have a look at this click here
The only way to be absolutely certain information is removed is to either incinerate the drive or take it apart and scrub the writing surfaces with steel wool.
Back even in pre-windows days, there were simple un-delete programs.
As has been said "deleting" merely removes one character from the "index", and so the operating system loses the reference to this file............. The oldest undelete programs listed the files it found with missing first characters, and left it to you to type the missing letter/number.
This would only work for very recent deletions, because any newly saved files often were recorded on this "space" on this disk, regardless of where the operator might think they would be.
There is no reason to believe that this has changed except files, disks and O/Ss are all much much bigger than they were.
If you look at the site I referred to above you will see there are different grades available. Several are for general use and thus obtainable by anyone. If you scroll further down the page there are special grades for law enforcement agencies which are not available to the general public.
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