secure deletion?

[BillGatesJR]

I've been playing around with some file recovery software to see how deeply they can recover deleted files, and it seems as though when you delete the file, the only thing that still exists is the file in it's latest modified state. So if you overwrite a file before deleting it, only the the replaced data will show up when you attempt to recover it. Is this a good tactic for beating police methods or can they also recover the older versions of files?

If the computer only retains the latest versions of files, then I was going to write a batch file that uses the dir command to collect all of the filenames in a directory, and then overwrite every file in the list with zeroes before deleting them.

[Joe Camel]

I think I read somewhere for it to be really secure you have to change every value to zero, like you said. I'm no computer scientist though. I'm interested in this too though, and I thought when you deleted something it was just hidden from the operating system, but still on the hard disk?

[Transparent]

I've always used Sure Delete whenever I delete sensitive material. You should test out how effective it is at deleting files permanently.

[BillGatesJR]

Originally Posted by Stendhal Syndrome

I think I read somewhere for it to be really secure you have to change every value to zero, like you said. I'm no computer scientist though. I'm interested in this too though, and I thought when you deleted something it was just hidden from the operating system, but still on the hard disk?

It is still on the hard disk, hidden from the operating system like you said.

When you delete a file, the only thing REALLY being deleted is the file's namespace. (for instance, the name "C:\secretfile.txt" will be free to use when the file that this name points to is no longer on the operating system). The file itself won't be really deleted until that freed up sector is overwritten.

So the question is whether or not the original data in the file can recovered if that file was overwritten by a new file with the same exact name and extension.

If this is true, the task can easily be accomplished with a batch file. Just have the batch script delete the original file, create a new file with the same name, and then delete the new file.

[Joe Camel]

Originally Posted by BillGatesJR

It is still on the hard disk, hidden from the operating system like you said.

When you delete a file, the only thing REALLY being deleted is the file's namespace. (for instance, the name "C:\secretfile.txt" will be free to use when the file that this name points to is no longer on the operating system). The file itself won't be really deleted until that freed up sector is overwritten.

So the question is whether or not the original data in the file can recovered if that file was overwritten by a new file with the same exact name and extension.

If this is true, the task can easily be accomplished with a batch file. Just have the batch script delete the original file, create a new file with the same name, and then delete the new file.

I'm pretty sure the batch file idea will work, I also remember reading something about the old file is gone when it gets overwritten after deletion, like you said.

I'm not 100% sure though, just trying to help.

[Syphilis]

If you have the file overwritten, it can't be recovered, and nothing will show up if you search for undeleted files, because it doesn't exist, and it's been overwritten by random data.

[BillGatesJR]

Originally Posted by Syphilis

If you have the file overwritten, it can't be recovered, and nothing will show up if you search for undeleted files, because it doesn't exist, and it's been overwritten by random data.

I used DiskDigger to search my hard drive after testing my batch script on a text file. I just typed a Hello World message in the text file, deleted it using the script, and tried to recover it with this software. The file is there, but the data is gone. It has been replaced with some meaningless random numbers.

If you want to try this yourself I can post my batch script on here. Try it with several recovery programs. I haven't found a single program that has been able to recover the original data.

The batch script for overwriting and deleting a file is:

echo off
echo %random%%random%%random%%random%%random% > %1%
del %1%

All you have to do is open command prompt, navigate to where you have this batch script saved at and type

mybatch.bat filename

Press ENTER and it is gone. Try to recover it with any software you want. Oh and by the way, this simple script will not accept wildcard characters.

This is because the script uses the same filename to create a new file, and if you used a wildcard like *.txt, it will try to create *.txt which is obviously not valid.

But I hope to improve this script so it can delete multiple files on a wildcard parameter. The only way I can think of for this to be possible is if the batch uses the dir operation, stores the filename list in a textfile, and overwrites/deletes every file in the list from top to bottom, then overwrites/deletes the temporary file list.