Eternal Sunshine of the Spotless Drive

Completely wiping the contents of your hard drive is a tough task. But there are tools that make deleted data very hard to reconstruct

Reader Gary Anderson asks a question that has crossed the minds of just about anyone who has parted ways with a used computer: I plan on giving my old laptop to a colleague but am nervous about the sensitive data that may inadvertently be left behind. How do you suggest I effectively clear my computer of this information?

This seems to be a subject that people worry about either too much or too little, blithely discarding computers without concern for the data still on them or else becoming paranoid about scrubbing away all traces. The problem is that merely deleting files from a hard drive doesn't remove the contents from the disk. Until new content saved to the drive overwrites the old files, they remain readable with relatively little trouble.

Various software steps can make the contents progressively more expensive and more difficult to retrieve. But unless the disk is physically destroyed, the contents can be reconstructed, if necessary by examining the disk platters bit by bit with a scanning electron microscope. Fortunately, even relatively modest recovery efforts can cost thousands of dollars, and the most extravagant ones can run into the millions. Most of us have nothing on our hard drives worth anywhere near that much.


 The National Institute of Standards & Technology has just issued a report, "Guidelines for Media Sanitization" that advises government agencies on how to clean up digital storage media for disposal or reuse. It examines techniques ranging from simple clearing of the data to ones that involve the terms "disintegrate, shred, pulverize, or incinerate."

The happy news: "Studies have shown that most of today's media can be effectively cleared and purged by one overwrite using currently available sanitization technologies," according to the report.

This still calls for something more than simply deleting the files. On Microsoft's (MSFT) Windows, you'll need some software that systematically overwrites the contents of the drive. Eraser is a free tool (you can find it on that will do the job. If you're an Apple (AAPL) Mac user, the built-in OS X Disk Utilities has a feature that will safely overwrite file contents.

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