Hitting that delete key on the keyboard sends a file from your hard drive to some magic holding area called the recycle bin or trash. But after you "empty" that refuse bin, those files are gone forever, right? Not quite. Sometimes when a user needs to be sure a file is really erased — a sensitive document or financial information, for example — an extra step should be taken to ensure files are really gone. In this feature, we'll show you the best ways for Mac and Windows users to securely erase individual files, and securely format hard drives for free.

 

Delete isn't actually deleting?

An oddity of hard drives is that a file isn't actually obliterated when it's deleted. On the plus side, this means files that are accidently deleted aren't really gone and can be recovered. On the minus side, this means that files that users would rather have be permanently deleted can be recovered.

Instead of immediately obliterating a file, a hard drive simply marks a file from "protect this block of information," into "feel free to write over this information." Depending on how many files are written to a drive, how large the files are, and other mitigating circumstances, a file could actually stick around on a hard drive for a very long time after being "deleted."

Securely erase files

Mac users have a pretty easy time of securely deleting files. After a file, or group of files, is moved to the trash, in the Finder menu, select Secure Empty Trash. This command will mark the files as deleted, but will also write zeroes to the hard drive, making file recovery more difficult. Since files are actually being written to the drive, instead of simply being marked as "able to be written over," Secure Empty Trash takes longer than the regular Empty Trash command.

On the Windows side, there isn't a tool built-in to the operating system to help securely delete files, however there are many freeware programs out there to help users out. One of our favorites is from Heidi software; it's simply called Eraser. Eraser adds an item to the right click menu, allowing users to either fully erase the recycle bin, or individual files. Eraser takes specified files, marks them as "able to be overwritten," and then writes random data to the places where the files were. Again, it'll take much longer than a normal deletion would take, but the data should be secure.

Securely format a hard drive

Instead of simply throwing a hard drive or computer in the trash, think about either recycling it through a recycling program or donating it to a local school or charity. However, before donating the machine, you'll want to securely erase the data from the hard drives so that your data doesn't end up in someone else's hands.

Much the same way that deleting a file doesn't actually remove all the data, formatting a hard drive also doesn't overwrite all the data either. Typically when a hard drive is "formatted," areas of the disk are simply defined into logical groupings and some sort of index defines how the disk is divvied up. Formatting a hard drive adjusts the index to the new specifications, but doesn't actually touch the data.

Fortunately, there are tools to scrap the data. For all OS users, we'd recommend pulling the hard drive if possible, and connecting it to another computer from which you can boot. This will ensure that you're able to delete all the data without being interrupted by the currently running operating system. If that's not possible, try to find a bootable CD, then run an MS-DOS utility like Killdisk and get your erase on.

Mac OS X users will find a secure erase tool as part of the operating system. Simply head to Disk Utility, select the partition you'd like to erase, and then select the "erase" tab. Under the Security Options button, you'll find a litany of options for securely erasing a hard drive.

The first simply zeroes out the data. This process is relatively quick, though much slower than a standard "format," and will provide an adequate amount of security on deleted data. To go the extra mile, OS X provides users with two other options including a seven pass erase which writes random characters seven times over, or a 35-pass erase, which writes and rewrites data 35 times over. If we were getting rid of one of our main work computers which contained our financial records or other sensitive material, we'd likely set the erase for the 35 pass erase and let the computer do its thing overnight. No point in not being as secure as possible.

On the Windows side, go with the aformentioned Eraser product to erase external hard drives. First, you'll want to format the drive just like normal, so right click on the drive and select "format."

It'll bring up a regular format dialog box, and feel free to simply select "quick format."

Now that the drive is empty, right click again and select "Erase unused space." A confirmation dialog box will appear with options. Simply click OK and you're on your way to securely erasing your hard drive.

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[images: Jon A Ross, mihimaru, Gary J Wood]