Why is permanently deleting a file without any trace of it left on the system is considered to be a really complicated process?

Question

I got the basics. Deleting a file simply tells the system that the sectors it occupied are now available for new data to be written on.

But if you want a more secure deleting why cannot you just overwrite everything with zeroes? If the computer system is only working at its core by manipulating zeroes and ones, why is it said that physically destroying the drive the information is stored on, is the only secure way to make sure nothing is left on it?

In: Technology

Answer 1

It depends on how the information is stored. In a traditional hard drive with spinning platters, the drive writes to the platters by changing the magnetic characteristics of a part of that platter to a north or south, one representing a 1 and the other a 0. It also records everything to a table of contents so it can just refer to that table of contents when looking for it. When it deletes something, it just deletes it from that table of contents showing the once occupied space as free. That information is still there and not turned into all 0s when you delete it. It’s there until new information is written and the drive decides the information needs to be written where the old information resides.

There is software that can scan every “free” section of the hard drive and rebuild the table of contents as long as those sectors aren’t overwritten and extract those files. There are also commands you can perform to write all 0s or random 1s and 0s to the drive. Once either one of these is done, extracting information from the drive becomes exponentially harder. If the old information was 1001 and the overwritten random digits are 1010 you can painstakingly analyze every sector of the drive and see how strong the 1s and 0s are to try to extrapolate what was originally on there. If you read each sector and find it shows 1.0000, 0.0001, 0.990, and 0.0100 you could make some inferences as to what used to be there. Again, this is an extremely slow, tedious, and expensive process. No one is doing this to hard drives they bought on eBay to reconstruct your old hentai fanfiction. Governments and billion-dollar corporations do this to find secrets from drives that have been improperly disposed of.