I tend to collect old computers around here. I am asked by friends and family to get them to an appropriate eWaste drop off when retiring the computer or replacing it with a new one. Of course, we don't wan't any old data rattling around on there -- just in case -- so I need to wipe all the data from the computer before I take it in.
I recently had 3 machines to clean off, so I turned to an old friend, Darik's Boot and Nuke (DBAN), available to download for free from their web site. DBAN is a LINUX-based boot disk that can startup most computers, both Windows and Intel Macs. Then, in a few keystrokes, you can tell the software to erase the data on the internal hard disk and write blank information to it 3 times. This type of "wipe" is sufficient for most home users (and many small businesses) as it would take some very high-end skills and equipment to recover the data. For me, DBAN is certainly "good enough" protection that someone isn't going to stumble across any personal data on the computer once i send it away.
Here is what the web site has to say...
DBAN is a self-contained boot disk that automatically deletes the contents of any hard disk that it can detect. This method can help prevent identity theft before recycling a computer. It is also a solution commonly used to remove viruses and spyware from Microsoft Windows installations. DBAN prevents all known techniques of hard disk forensic analysis. It does not provide users with a proof of erasure, such as an audit-ready erasure report.
If you need more powerful data erasure and/or proof of deletion, Blanco also provides such services for a fee.
DBAN can only work if the machine can power up and still has a working CD/DVD drive or USB port (for flash drive boot). If the computer no longer operates then removing the hard drive and connecting it to another computer is the only way to erase the data stored there.
From the DBAN web site you can download a CD disk image that can be burned to a blank CD (or installed on a Flash Memory Drive) and then used to book the computer you need to erase. Windows users can simply double-click the image file to be prompted through the burning process. Mac users may require a bit more knowledge, as they will need to use the Mac Disk Utility included with their computer to create the boot CD.
Once the CD is burned, you insert it into the older computer and instruct it to boot from the CD instead of its local hard disk. On many system you will be promoted to "Boot from CD" automatically when it detects the CD.
I usually simply select the defaults for data erasure and then let the program run. Depending on the speed of your computer and, more importantly, the speed of your hard drive, it can take several hours to complete the process.
DBAN Startup screen - Hit ENTER To continue
DBAN screen to select hard drive to erase - Tap SPACE to select drive and then F10 to start erasure
DBAN erasure screen with estimated time remaining
If you are donating a computer, or retiring it completely and taking it to an eWaste Drop Off, do yourself a favor and use DBAN to erase the hard drive completely before you do. It can prevent your personal data from easily falling into someone else's hands.