I DBAN’d my laptop a while ago and was told that I have to scan over and replace every bit of the hard drive multiple times or else hackers could still get the data. How are they able to do this?
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When your computer writes a file to a hard disk, it does two things: it writes the data to a location on the disk and it makes a record in a master data table so that the information can be found again and protected from overwrite.
When you “delete” a file, your computer changes the record in the master data table so that the file will be skipped in searches and the space that it takes up is available for overwrite. The information is not deleted in any real sense. A skilled person who has access to the drive can easily rebuild the master data table and get at the information if it has not been overwritten. This can be done remotely by hackers.
To secure against that you would use a scrubber. That is a program that overwrites the data with zeros or random data and depending on its level of sophistication does a bunch of other things too.
Usually, the scrubber makes several passes changing the data multiple times. It has been rumoured for a long time that physical examination of the hard drive may enable someone to unscrub data. I can’t say if these rumours are true or not. If they are, then I would speculate that they would require physical possession of the hard drive.
DBAN looks like it is a very basic and free scrubber. If you look on their website you will see all the things that their paid app, Blancoo Drive Eraser, does that the free version does not. I say ‘looks like’ because if your data is sensitive enough that it requires scrubbing, you really shouldn’t rely on a third party to scrub it.
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