Data Recovery Digest

Typically when you delete a file on modern operating systems, the link pointing to that file is actually deleted, not the file itself. That means the file is most likely still on the hard drive and is the reason why there are so many free data recovery tools. Now, it may seem ludicrous that files aren’t actually deleted since the hard drive will eventually get full, but when the link to a file is deleted, the hard drive is free to over write it when it needs the space. For typical people in most circumstances, this is fine and it’s no problem that it will be some time before the file is actually overwritten. But sometimes you want to not only delete the link to a file, but also permanently delete a file from the hard drive.

In order to permanently delete a file, the link to the data needs to be deleted and the data needs to be overwritten with new data. A number of modern operating systems include tools to permanently delete a file and there are many paid and free apps available too. Mac OS X has the option to securely empty the trashcan, meaning to permanently delete the files. It also has a disk utility tool that helps securely remove files. Linux and some other Unix based operating systems have a command line program called “shred” that will permanently delete files. Shred does a good job, but if you want to be extra safe, you can manually overwrite the disk space the file resides on with zeroes. To permanently delete files on Windows, you’ll need to run an application like Cipher.exe, BCWipe, or File Shredder. There are many professional and open source applications and each one is a little different.

The methods programs use to delete files vary, but I’ll cover a couple of the common methods. The first, which shred uses, is to select random lines in a file and overwrite them multiple times with random data in hopes of corrupting the data enough to make it unusable. This has some drawbacks, since not every line of data is overwritten. Other methods will just overwrite all the data with zeroes.

There are two main standards for deleting data. One is US DoD 5220.22.M, and as the name implies it is used by the Department of Defense. This method overwrites data with random data 7 times. A more secure method is the The Gutmann Method that overwrites data with certain patterns of data 35 times.

The most sure-fire way to permanently delete files is to physically destroy the hard drive. Physical destruction is more involved than simply running a program and can be more difficult. There are a number of ways to do this, but some of the most secure ways include driving a metal spike through it, taking apart the platters and running a high-powered magnet over them, burning the drive, or using a highly corrosive chemical on it. To be extra safe, you could even run a software program that is US DoD 5220.22.M compliant and physically destroy the disk for extra protection.