I overheard two young guys most probably college students, talking about deleting files such that nobody will ever read that file again. This happened as I was sitting in a corner next to a coffee shop in Baguio City where a free WI-FI is available as I need to use my iPAQ to check my emails.

One guy advised to the other that after deleting a file, he should Empty the Recycle Bin to make sure no one will ever read that file again.

I just smiled and hoped that this guys will stumble upon this blog and be able to understand that their assumption is wrong.

Deleting a file in Windows does not actually delete the content of the file. It just removes the reference of the file in the file system so that you can no longer see it and the space used by the file will be re-used when Windows needs a space to write something. As long as the space used by the deleted file were not yet overwritten, you can still recover the contents of the file by using undelete tools like the FREEUNDELETE tool. I suggest you download this tool as it may come handy when you need one.

So how do we delete a file such that it will very difficult if not impossible that one will ever read the contents of that file again?

One answer is presented by Peter Gutmann in his paper. It proposes a technique to overwrite the content of the file 35 times with random and fixed pattern. Take your time to read this paper. You would be amazed how data is written into your hard drives and how it can be recovered.

A free, open source program that implements Gutmann technique to securely erase a file is Eraser. It was originally written by Tolvanen.

So next time you delete a file in your computer and wants that no one will ever read the contents, think again.