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Reformatting does not completely erase all traces of files from a hard drive but, so far, no viruses are known to be able to recover from a reformat. Repartitioning does something all together different.

I have assumed for years that a delete/repartition and reformat of a hard drive will wipe it clean. I've done this to web viruses; recently one that put itself into the drive system folder that couldn't be removed by Norton or manually. So my question is does repartitioning and reformat of a drive clean it?

In this excerpt from Answercast #10 I look at reformatting and partitioning a hard drive, how thoroughly it cleans a machine, and the effect this will have on your computer.

Cleaning a hard drive

The short answer is, "It depends."

It depends on what you are attempting to do.

  • A reformat of the drive deletes all the files; which means that any file that existed on the machine is no longer referenced and all of the data will (presumably) be overwritten by whatever you subsequently write on the disk.

  • Partitioning, repartitioning the drive, or changing the partitions (in other words, if you're making the partitions smaller or larger) can make it less recoverable.

Reformatting may be recoverable

The problem is that formatting a hard drive may not actually erase the contents of the sectors. It's very much like deleting a file.

It would be possible, in many cases, to "unformat" using some utilities that can do that; or to actually use forensic tools like Recuva that will allow you to go in and undelete files.

In other words, the free space that you've just created could potentially be analyzed and the files that used to be there recovered.

Recovering from a virus

Now, if you're looking at this as a way to save yourself from a virus, formatting is fine. It certainly does this "delete function" that you want.

I know of no malware that comes back from deleted files.

So, in that sense, formatting the hard drive works just great.


Partitioning adds to the mix in that (depending on which partition you are dealing with) a repartition of the machine - into the same partitions it had before - doesn't really change a whole lot. It doesn't make things more or less secure.

Changing a partition's size will impact the partition that follows it, making it less likely to be recovered; but unless you're actually moving partitions around on the hard disk I don't see an advantage to partitioning.

If you're really concerned, and I mean REALLY concerned, about making absolutely sure that not only are the files deleted, but that they are also not recoverable, then I would look into a tool such as DBan. That will not just delete the files, but override all the free space so that the files can't ever be recovered.

Nothing is going to survive that.

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Article C5223 - April 18, 2012 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

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1 Comment

April 20, 2012 1:19 PM

I found a free diskwipe app from Big Angry Dog called HardWipe that totaly, completely wipes a drive, everyhing, using the alogarithms you pick.
I tried it on an 80Mb SeaGate I had and it works just fine. It takes a while.

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