TTFA2: Securely Delete Files

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Securely Delete Data and Files

During the controversy over the Iran-contra affair, in 1986, Lieutenant Colonel Oliver North attempted to erase all the relevant e-mail messages on his computer; he repeatedly pressed the DELETE button, thinking that he was thereby expunging the messages. "Wow, were we wrong!" he later observed.

After reading this chapter you will be able to;

  • Delete files and data securely so that no-one will recover them

With a harddisk even if you erased every piece of data, it is sometimes possible with (very) specialized hardware to recover pieces of the data. If the data is very confidential and must be erased with the greatest care, you can use software to "overwrite" all pieces of data with random data. When this is done multiple times, this will make the data untraceable.

Securely delete data under Windows

For Windows there is a good open source tool called "File Shredder". This tool can be downloaded from

Securely delete data under MacOSX

There are basically to build-in steps to make to securely delete your data on Mac OSX.

1. Erase the free-space on your hard-drive containing all the data of items which are deleted in an unsecure way.

2. Make sure that every file from then on is always securely deleted.

We start with the first one:

Erasing Free Space

1. Open Disk-Utility which resides in the Utilities folder inside the Applications folder.

2. Select your hard drive and click on 'Erase Free Space'.

3. Three options will appear, from top to bottom more secure, but also they take much more time to complete. Read the descriptions on each one of them to get an idea from what will happen if you use them and then choose which one might suite your needs the best and click 'Erase free Space'.

If time is no issue, then use the most secure method and enjoy your free time to get a good coffee while you Mac crunches away on this task. If the crooks are already knocking on your front-door you might want to use the fastest way.

Securely Erasing Files

Now that your previously deleted data is once and for ever securely erased you should make sure that you don't create any new data that might be recovered at a later date.

1. To do this open the finder preferences under the Finder Menu.

2. Go to the advanced tab and tick 'Empty trash securely'. This will make sure that every time you empty your trash all the items in it will be securely deleted and are really gone!

Note 1: Deleting your files securely will take longer then just deleting them. If you have to erase big portions of unimportant data (say your movie and mp3 collection) you may wanna untick this option before doing so.

Securely delete data under Ubuntu/Linux

Unfortunately currently there is no graphical user interface available for Ubuntu to delete files secure. There are two command-line programs available though.

  • shred
  • wipe

Shred is installed in Ubuntu by default and can delete single files. Wipe is not installed by default but can easily be installed with using Ubuntu Software Center or if you understand the command line you can install it with apt-get install wipe. Wipe is a little more secure and has nicer options. It is possible make access to these program's easy by adding it as an extra menu option. There is more information on this here.

What Next?

  • Try out some of the software and techniques listed here.
  • Spread the word about how to securely delete files.
  • Try running a workshop on how to securely delete files