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How to Completely Erase Computer Files

Whether you recycle your old computer, sell it, give it away or take it to the dump, you may also be giving away personal information, even if you think you erased everything on your hard drive.

Two MIT graduate students bought 158 used disk drives on the secondary market and found many “had not been properly sanitized.” They found personal information, even when the previous owner had attempted to erase the data or even reformat the entire drive. The pair, Simson Garfinkel and Abhi  Shelat, found medical records, love letters, pornography and thousands of credit card numbers.

The researchers aren’t the first to discover a treasure trove of personal information on used machines. In 2002, a journalist purchased a used computer at a thrift store that had once belonged to the U.S. Veterans Administration. The drive contained medical information including the names of patients with AIDS and mental health problems.

While some people make no effort to delete sensitive data, others are lulled into a false sense of security by using standard file deletion methods. Most are temporary at best. The most common way to delete files in Windows and Macintosh is to drag the file into the Mac“trash  can” or Windows’ ‘recycling bin.”  While that removes it from the desktop it does not remove it from the computer. In fact, you can restore the file by simply opening the trash or recycling bin and dragging it back to the desktop.

Both the Mac and Windows allow you to go one step further by emptying the trash which appears to delete the file completely. The Mac, for example, asks you if you are sure “you want to remove the item in the trash permanently.”  Windows asks if you’re “sure you want to delete all of the items in the recycling bin.”  But neither method is permanent. Erasing a file doesn’t actually delete the data; it just removes the file name from the directory. The data is still there.

Deleting a file the standard way is a bit like crumpling up a piece of paper and throwing it in the trash can rather than running it through a shredder. The MS-DOS delete command doesn’t have an obvious “undo” feature but it too can easily be reversed.  This can be good news if you’ve accidentally deleted something. But it’s bad news if you want it permanently gone. Numerous software products are available that allow you to “undelete” such files.  “Undelete’’ from Executive Software is one of many that will allow you to recover deleted files on Windows. There are versions of Virtual Lab data recovery software for both Windows and Macintosh.

PCWorld has a video on how to completely wipe data from a PC’s hard drive and MacWorld has published an illustrated tutorial on how to wipe a Mac’s hard drive.

Data Shredding Programs

Iolo Drive Scrubber


OnTrack Erasure Software

Deleting Data on iPad/iPod

This article from Apple’s support website explains how to use the Settings > General > Reset function to erase all content and settings

CNET’s Donald Bell has produced an excellent video on how to backup and erase iPads and iPhones.  This includes ways to use iTunes to backup and restore the device as well as ways to just quickly erase it from within the iPad’s settings menu.





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