Physically destroying a disk with a hammer won't prevent the really clever bad guys from getting at the data. They are quite capable of reading data from fragments of a disk.

But - it's very expensive to do.

The same is true of a disk that has been erased using a properly-written disk erasing application. The data can still be read, but not by using an application. The really clever bad guys dismantle the drive and examine the surface using some very expensive kit.

BTW, be careful when physically destroying a modern disk. The platters are sometimes made of very thin glass, and you really don't want tiny fragments of that getting under your skin or into your lungs.

So its fine to use a good disk erasing application. The question then becomes "what is a good disk erasing application"? Well, its one that amongst other things, repeatedly overwrites each and every sector on the drive with various random data. I use Darik's Boot and Nuke, known as dban.

If you *really* want to be sure your data can never be read, then the only sure way is to physically destroy the disk by putting it into a physical hard disk shredder.

PPD

SoCal,

Not really interested in making a personal level argument out of this.

Guess we'll have to agree to disagree on our points of view on the matter.

My 2 cents.

The original poster did not say to whom he/she is selling his/her laptop.
So let's keep it in perspective. More than likely the laptop will be sold to
someone the seller already knows.

Assuming that, I don't think the seller needs to jump through hoops in trying to destroy what personal data he/she may have on the laptop: a simple reformat of the hard drive would suffice.

No?

"It depends".

There is a very profitable cottage industry in certain African countries based around extracting stuff from the hard drives of old computers. I don't know how much effort they put in before they get something useful, but I've seen the film.

If I give away an old PC, it goes without a hard drive. The hard drive either goes into one of my existing machines, or a caddy, or is treated to some sledgehammer reformatting before being buried in the garden.

My daughter had my last laptop. I bought a used hard drive for £20 and installed that, plus all the software. The original hard drive is now pushing up daisies.

Can someone explain (simply please) how data can be recovered from a disk that has been zeroed.

For example say my PIN is 4567, the binary, as it is stored on the disk is :- 1,0,0 1,0,1 1,1,0 1,1,1
After zeroing, surely this becomes 0,0,0 0,0,0 0,0,0 0,0,0 so how is it possible to reconstruct my old PIN number?

Latency....................

I merely answered the question as it stood, obviously the more times you overwrite a disc position then the less the latency effect.

If selling it within the family or friends circle then an erase of all sensitive info and an erase of free space with a programme like Eraser should suffice.
If you are selling to an unknown then for the sake of £30 it might be better to replace the disk. My laptop takes 5 minutes tops to replace the the disk. I'd rather do that than go through the erase hassle.
The last one I sold I replaced the hard drive with one from an old work laptop. No personal information on it anyway (and nothing sensitive from work either).
Mind you I replaced the hard drive more for ease than security.:}
I'll leave the paranoia to others....

If you have the original OS disks I highly recommend "Boot and Nuke" .

A Google search will bring it up top of the list :ok:

If you store your pin number on any computer, you're wrong.
If you store bank account information on any computer, you're wrong.
If you store your social security number (U.S.) on any computer, you're wrong.
And if you store the names of your children (if you have any) on any computer, you're wrong. (Many, many people use passwords either containing part, or all, of one of their childrens' names or some combination thereof.)

A single pass of an erase tool is more than sufficient to make the drive unrecoverable when dealing with modern hardware. All this "35 pass" stuff is completely unnecessary and takes a huge amount of time to run. If you really want to know how good a single pass is, pick up the phone to the most expensive data-recovery firm you can find (Vogon are very good and also very expensive), tell them you've just run a DBAN single-pass wipe and see if they'll quote you for recovery.... not a chance in hell.

Thanks for some sense Shunter.

From Kroll

"One of the most common reasons people send their disks to Kroll Ontrack is because they have reformatted a drive without realising that there's essential information on there. While it doesn't have the facilities to resurrect data from a drive that has been zeroed out - had information rewritten over every sector - most people don't do this when erasing hard disks, so Kroll Ontrack can simply ignore the missing directory that gets trashed during a standard format and examine the contents of the disk sector by sector."

From OnTrack

"Physically destroying the hard drive is the best way to make sure the data is gone for good. Fortunately, there are other safe ways to ensure data is securely erased. Data-erasing software products will overwrite data, with a single pass usually being sufficient. Military norms, however, require that a drive be overwritten several times. In these circumstances, even Ontrack’s data recovery engineers would be unable to recover useful data. The cost to attempt such a recovery would also be tremendous.

Data-erasing software products also provide a better way of wiping out data than carrying out a low level format. Not only are they more user-friendly, but they also are more reliable. Low level formatting tools will zero-out every sector of the drive once, while with data-erasing products such as DataEraser™3 you can define a number of overwrite passes (from one to ninety-nine) and select the overwrite pattern."

Mac

:ok:

I have three old hard drives from computer upgrades. Got a P C shop to check them for bad sectors etc. Then bought three external drive cases, formatted the drives and now use them to store data such as family history and photos.
Maybe what was on the drives originally is still there, but it is a way of utilising them for external storage.

It doesn't - every time I've re-installed an OS from a recovery partition, letting it do a reformat, all sorts of password data, log-ins etc pop up uninvited when I reinstall the various programs.

I think they sneak into an alternate universe while the reformat goes on and then climb back onto the hard disc. But I might be wrong.....

Recovery partitions are the work of satan. They do whatever the vendor wants them to do, and that's usually not a reinstall. Unless they reformat the OS partition (which they commonly don't) your info if likely going to pop straight back up again when the process has completed.

They are an excuse given by OEMs not to have to give you a Windows CD. Personally I don't like having a chunk of my hard drive space devoted to these stupid recovery partitions.

No messing. BBC News - Four mechanical ways to destroy disk data

I've had problems with previous computers, yet never ever been advised by the help line to use the recovery aspect of the hard drive (the most useful advice I received from one helpline guy was to switch off, remove the battery and wait 30 seconds before replacing the battery and powering-up the system). Whenever I've asked about the recovery partition I have been told 'forget it' and I've never found instructions anywhere as to actually how or when it might be useful.

What I have done (when my hard drive was warning of impending failure) was to remove the hard drive and get it cloned by PCW*rld onto a new (larger capacity) hard drive.