Did you know that when you delete a file on your computer it isn't really deleted? Your computer marks the space the file uses on the hard disk as available, but the file is still there. The good news is that you can easily recover the deleted file — if you catch it before your PC overwrites it with another file.
The bad news is that when you sell old computers or send them to be recycled, your files are easily-recoverable. Passwords, sensitive documents, emails are easy pickings: all it takes is a snoopy person with readily-available recovery tools. Before you let old computers out the door, you should wipe all hard disks securely.
But what if you don’t want to wipe an entire hard drive? More good news: you can also securely delete individual files.
In this article we'll look at open source software options for securely wiping hard disks, and secure file deletion.
Delete Files and Hard Drives with Open Source Software
Darik's Boot and Nuke
Darik's Boot and Nuke (DBAN) is our first choice for securely wiping hard disks. DBAN is a self-contained system that you download and copy to a CD, then boot the CD on the system you want to securely erase. DBAN doesn't care what operating system you use: it works on all of them, Linux, Mac, Unix, Windows, you name it.
Figure 1: DBAN detecting a laptop hard drive and a USB flash drive.
DBAN completely wipes the contents of SATA, IDE, SCSI, and SAS hard disks, and some USB and Firewire-attached storage media as well. In other words, pretty much any kind of hard drive or USB drive attached directly to your computer.
You can boot up DBAN and explore without hurting anything: Press F2 to learn about DBAN, F3 to learn some optional boot commands, and F4 to read about what to do with disks in RAID arrays. (A RAID array combines multiple hard disks so they act as a single unit.) DBAN is not capable of operating on a functional RAID array; you have to dismantle your RAID configuration and operate on each disk individually.
Back at the main DBAN screen, press the Enter/Return key to launch DBAN in interactive mode. This won't delete anything; you're still just looking around at this point. If DBAN detects more than one drive, use the arrow keys to navigate to the one you want to erase, and then press the space bar to select it. The word "wipe" appears on the one you choose.
At the bottom of the screen you'll see your erase options: PRNG, Method, Verify, and Rounds. You can safely look at these without accidentally erasing anything, because you have to press F10 to start secure deletion. Let's take a look at these options.