Just like Windows, OS X provides built-in tools to securely remove data off your hard drives. While these tools are effective on hard drives, securely removing data off your SSD (solid state drive, found in all newer Macs) is a bit more complicated, which makes the tools I mentioned about above largely ineffective.
We’ve previously mentioned Apple’s Filevault, which you can use to secure/encrypt your files, but if you find the need to delete your sensitive data, then you can follow any of the methods detailed below.
What Happens When You Delete a File
First, let’s go into detail a bit regarding what happens when you click “Move To Trash.” That’s exactly what happens in the background; OS X moves the selected file(s) to the Trash folder on your Mac. No files are deleted, no entries are removed, and more importantly, no disk space is freed up. OS X simply moves the file(s) from their original location into a separate folder named “Trash” and found in your user directory “/.Trash.”
Whenever you click on the Trash icon present in your Dock, OS X opens the Trash folder. Here you can see everything you’ve moved to the Trash; drag out files to recover them or click the “Empty” button.
It’s a general observation that when you click on “Empty,” you can no longer see the files, hence you think that they have been “deleted/erased.” In fact, they aren’t really gone. Under the hood, only the file system links to files in the Trash are removed.
What that basically means is the underlying data in a file is dissociated/removed from the names and parent folders that used to lead to them, hence they don’t exist in a particular place, and OS X can’t identify them. However, even if you can’t find them, they still exist on your hard drive, at least for a little while.
Why Does Your Disk Space Free Up After File Removal?
Once the data blocks have been removed from a file, OS X treats it as unused storage. That is why deleting files frees up disk space. When the time comes to store a new file, OS X simply overwrites the space previously taken up by the unlinked (deleted) file.
This is a good thing as well as a bad thing. In the case of an accidental data loss, depending on how large your hard disk is, the previous “deleted” files may be overwritten in a few seconds, a few days, or even a year, so it’s sometimes possible to recover an accidentally deleted file using the unlinked data present.
But it also means that a thief could potentially access the files you may have deleted, or reselling a Mac with data you thought you had deleted may have bad consequences.
Using Secure Empty Trash
The easiest way to securely delete any sensitive data on your Mac is by using Secure Empty Trash. Secure Empty Trash works quite similarly to the normal Empty Trash, but it adds an important extra step. Before unlinking your files, OS X overwrites them with meaningless, randomly generated data.
If anyone tries to recover your data, they’ll find a block of unusable information where your data used to be. In practice, OS X reduces the time between your files being deleted and being overwritten by the system; they are overwritten immediately with random, useless data, which is in turn eventually replaced with a new file.
To securely empty your trash, you need to access the Terminal and enter some commands.
Securely Erase an Entire Disk
You can also erase the entire contents of a disk or partition securely using Disk Utility. After choosing the disk on the left and selecting the “Erase” option, click on Security options.
The slider that appears is similar to the one found in Erase Free Space. Choose the far-left position for zero random overwrites (non-secure) or the far-right position for the Most Secure delete. You can vary between these two extremes using the options found in between.
The entire contents of the disk will be erased, and your data will be securely overwritten the specified number of times.
Storing important data isn’t really a good idea in this age of data infiltration and hacking, but it’s nevertheless a necessary for many. Using the tips above can help you save any sensitive data from prying eyes while deleting it. As always, it’s better to be safe than sorry.
Let us know in the Comments section below if you face any difficulty or if you have any suggestions or comments.