Can Computer Files Ever Be Completely Erased?

Posted on June 30, 2005

Slate has a good article that discusses how difficult it is to actually erase a file on your computer. Sure you can delete the file and empty the recycle bin but the data from the file is still there in your computer's hard drive.

When you delete a file from a standard desktop computer, the file first gets moved to the "recycle bin" or the "trash," which means only that you've placed the intact data in a new directory. You erase the file when you empty your recycle bin. But even then, much of the information remains on the hard disk. Exactly how much depends on the type of computer you're using and which operating system you have.
But what about programs like Eraser and Evidence Eliminator that write over the data on your hard drive and delete the path to the file on your computer? Slate writes that computer forensic experts say data can still be found on PCs even after these programs have been run to write over the data on your hard drive.
They first "delete" a file in the conventional sense, and then they overwrite it with zeroes, ones, or random data. Finally, they erase the record of where the original file was stored on the disk. More advanced programs might overwrite the original with something less conspicuous than a string of zeroes, like an ordinary text file.

But even if you do wipe your disk successfully -- and overwrite each of your deleted files -- traces of the original data remain. Writing to a magnetic disk is not as precise as one might think; when you overwrite a file, the new version doesn't completely cover up the old. The leftover data can be read out with certain imaging techniques, like magnetic-force microscopy and magnetic-force scanning tunneling microscopy. Computer forensics experts say it's possible to recover data beneath dozens of layers of overwriting, and privacy fanatics talk about wiping their disks up to 35 times over to be absolutely safe.

It really depends on who ends up getting your old hard drive. If someone with advanced technology and skills gets they will probably be able to recover some data no matter how much time you spent trying to erase it. If a person with average skills gets your erased hard drive you might have nothing to worry about. It is best to crush and destroy the hard drive if you want to feel secure that no one will ever access the information on it.

Update: Google crushes and shreds its old hard drives, see here.

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