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janmc · Mar 22, 2004, 01:04 PM

I'm selling my trusty G4 tower to raise some extra cash

and want to make sure that all my personal info, applications etc are completely deleted. Is there an easy, secure way to do this? I'm also concerned because I have personal info tucked away in OS 9 as well. And to complicate things slightly, I have 2 harddrives (ie 2 startup disks) on the computer as well.

Any help would be appreciated!

(I'm not looking for FBI standard deletion - would just prefer not to have strangers reading my old emails)

typoon · Mar 22, 2004, 01:10 PM

Well just boot from CD and run Disk Util. that is about it and format it. Once you overwrite on the clean drive it will remove any trace of your old info. I doubt anyone will try and get it from the drive once it is formatted. If you are still worried you can wait while the drive formats all zeros on the drive.

Quick format a couple of times til the Drive is renamed untitled. then you know you've pretty much cleaned it good. after installing the OS just rename it Macintosh HD just to set it to defualt then all will be good.

::maroma:: · Mar 22, 2004, 01:52 PM

Or you can wave a nice big electromagnet over your drives*. That would clean them off real good!

(*Don't try this at home.)

janmc · Mar 22, 2004, 02:09 PM

thanks, will have a go at reformatting drive and then reinstalling software from scratch.

voodoo · Mar 22, 2004, 02:15 PM

22000

awaspaas · Mar 22, 2004, 02:41 PM

Edit: nevermind... I should have read more carefully!

awaspaas · Mar 22, 2004, 02:44 PM

There are some that feel data can *never* be completely removed from a drive. If someone is determined enough and have the technology, they can get stuff off pretty much no matter what. I had a particularly paranoid friend that drove nails through his old hard drives when they went bad just so nobody would get any data off of them.

janmc · Mar 22, 2004, 02:57 PM

wow - that is paranoid! i just don't want anyone to see personal emails from ex-boyfriends or whatever

but i don't think there's anything on the computer that could incriminate me in any way

i don't store financial info or anything on it.

porieux · Mar 22, 2004, 06:41 PM

Originally posted by awaspaas:
There are some that feel data can *never* be completely removed from a drive. If someone is determined enough and have the technology, they can get stuff off pretty much no matter what.

Yeah, I've seen those reports too, but I don't believe them.

You'll notice those people aren't around to help when you are trying to get your own data back

Besides, if it were true it would mean that we could store MUCH more data on hard drives then they are rated for.

Xeo · Mar 23, 2004, 03:09 AM

If you're paranoid, then just quick formatting isn't enough. Anyone can use cheap software to recover the data. Takes no work at all. So if you're worried the buyer is curious like that, then write zeros. It doesn't take that long. Then, they actually have to work to get the data back.

I would write zeros if I was selling. It's just enough to keep almost everyone but the government out (and they'd do it only if they thought it would convict you).

Tomster · Mar 23, 2004, 12:34 PM

How to wipe hard drives? A damp cloth and Pledge!

Seriously, if you want to totally overwrite your drive with zeros, just use the terminal.

dd if=/dev/zero of=/dev/disk0sx where x=your drive number

or you can use if= /dev/random if you want random numbers overwritten.

Turias · Mar 23, 2004, 12:37 PM

How is it possible to recover data once you have filled the entire drive with zeros?

Tomster · Mar 23, 2004, 02:03 PM

Originally posted by Turias:
How is it possible to recover data once you have filled the entire drive with zeros?

This is what I have read on the internet. Not sure if it goes down as an urban legend but here goes. The drive is overwritten, but the tracks of data on the drive are not perfectly seamless. It is possible to read the data between the seams, but only with very specialized equipment which the general public does not have. Again, not sure if this is real or not.

Xeo · Mar 23, 2004, 02:09 PM

Originally posted by Turias:
How is it possible to recover data once you have filled the entire drive with zeros?

As Tomster said, but shortened: Specialized equipment.

The heads of the drive itself cannot read it therefore no software-only solution can recover it. There are companies that you can pay to recover data from drives.

Cadaver · Mar 23, 2004, 02:41 PM

I agree about zeroing the drive. Whenever I sell a computer, I do a long format the drive and write zeros to the entire space available. If you're really paranoid you can do this two or three times. Pretty much eliminates anyone but the NSA (or in the UK, MI5/MI6) from accessing any data on it.

A simple "quick" format is not even close to being secure.

f1000 · 03:08 PM

Originally posted by Turias:
How is it possible to recover data once you have filled the entire drive with zeros?

An atomic force microscope with a magnetic tip can image the domains fringing a track.

The following is a representation of a track of 1010101 that has been overwritten three times with 0's (using periods to space the diagrams apart):

[ 1 ]............[] 0 []..........[]] 0 [[]........[]]] 0 [[[]
] 0 [............]] 0 [[..........]]] 0 [[[........]]]] 0 [[[[
[ 1 ]............[] 0 []..........[]] 0 [[]........[]]] 0 [[[]
] 0 [............]] 0 [[..........]]] 0 [[[........]]]] 0 [[[[
[ 1 ]............[] 0 []..........[]] 0 [[]........[]]] 0 [[[]
] 0 [............]] 0 [[..........]]] 0 [[[........]]]] 0 [[[[
[ 1 ]............[] 0 []..........[]] 0 [[]........[]]] 0 [[[]

Start............1st Wipe..........2nd Wipe..........3rd Wipe

As you can see, the original 1010101 pattern is still present along the outermost fringe of the 3rd wipe. This is why some scientists call magnetic media "palimpsests."

I'm sure there is specialized equipment that can do this much more quickly, but it is not something your average Ebayer is going to have in his house.

f1000 · Mar 23, 2004, 03:16 PM

Originally posted by Xeo:
I would write zeros if I was selling. It's just enough to keep almost everyone but the government out (and they'd do it only if they thought it would convict you).

I recall that some programs only zeroed the data tracks on a hard drive, but left the directory intact. You could still recover deleted filenames using a Hex editor.

Does anybody know if this is the case with OS X's drive utility?

Tomster · Mar 23, 2004, 06:16 PM

Here is a link to an article by one of the two MIT grad students who bought all of those used hard drives from swap meets, junk stores, and ebay. Quite interesting what they recovered.

Bottom line though, don't worry about it. Someone just bought your Mac. Their first concern is not the data on the drive, but whether there is anything wrong with the hardware they just bought. After kicking all of the tires, a prudent thing to do is to reformat the drive and reinstall the OS. No idea if there are any keystroke loggers on board set to fire off your data to some email account out there tied to a cron job.

Remember, they have just as much to worry about you leaving something illegal/immoral//damaging on the drive.

janmc · Mar 24, 2004, 10:56 AM

I'm not very experienced with OS 10 - if i use the terminal command option, is there anything that i can do wrong? i don't want to kill my computer! especially if i'll be getting money for it!
also - how do i find the drive number?

"dd if=/dev/zero of=/dev/disk0sx where x=your drive number"

Turias · Mar 24, 2004, 11:43 AM

Originally posted by Tomster:
Here is a link to an article by one of the two MIT grad students who bought all of those used hard drives from swap meets, junk stores, and ebay. Quite interesting what they recovered.

Interesting link, although I am even more interested in reading a technical description of what f1000 was saying, before.

(Sorry, those []]][0][[[], while somewhat informative, just weren't in-depth enough for mne. I want to know about the resistors, damnit!

)

Tomster · Mar 24, 2004, 12:10 PM

Originally posted by janmc:
I'm not very experienced with OS 10 - if i use the terminal command option, is there anything that i can do wrong? i don't want to kill my computer! especially if i'll be getting money for it!
also - how do i find the drive number?

"dd if=/dev/zero of=/dev/disk0sx where x=your drive number"

Type in df in the terminal. Wipe any partition you need. Your boot partition should be mounted at / All others are mounted at /Volume/drive name.

As for killing your computer, make sure you have a bootable dvd/cd because you will not be able to restart from it without installing a new OS.

Xeo · Mar 24, 2004, 12:10 PM

Originally posted by janmc:
I'm not very experienced with OS 10 - if i use the terminal command option, is there anything that i can do wrong? i don't want to kill my computer! especially if i'll be getting money for it!
also - how do i find the drive number?

"dd if=/dev/zero of=/dev/disk0sx where x=your drive number"

Don't bother with the command line option. Just use Disk Utility. You can choose to write random data 8 times and zero the drive for a total of 9 times of writing over what's there. That's more than secure enough. If the data on there needs to be secured even more so than that, melt the drive down, or at least break it in to parts, burn the parts, then drop each part to different locations in the ocean.

wataru · Mar 24, 2004, 12:25 PM

Originally posted by Xeo:
Don't bother with the command line option. Just use Disk Utility. You can choose to write random data 8 times and zero the drive for a total of 9 times of writing over what's there. That's more than secure enough. If the data on there needs to be secured even more so than that, melt the drive down, or at least break it in to parts, burn the parts, then drop each part to different locations in the ocean.

I read a while ago (on /. maybe) about a guy whose PhD project was basically a map of city infrastructure across the US. He made it entirely with publicly available information, and it was so detailed (and potentially useful to terrorists) that several times he almost got all of his work confiscated by the government. Anyway, the point is that once his hard drive failed, and to cover the tracks they zeroed, wrote random data, etc., and then froze the platters with liquid nitrogen, smashed them with a hammer, waved a huge magnet over the pieces, and then dumped them in some secure garbage dealy. Pretty impressive.

So there's always liquid nitrogen for the hyperparanoid.

Turias · Mar 24, 2004, 12:27 PM

Originally posted by wataru:
I read a while ago (on /. maybe) about a guy whose PhD project was basically a map of city infrastructure across the US. He made it entirely with publicly available information, and it was so detailed (and potentially useful to terrorists) that several times he almost got all of his work confiscated by the government. Anyway, the point is that once his hard drive failed, and to cover the tracks they zeroed, wrote random data, etc., and then froze the platters with liquid nitrogen, smashed them with a hammer, waved a huge magnet over the pieces, and then dumped them in some secure garbage dealy. Pretty impressive.

So there's always liquid nitrogen for the hyperparanoid.

That's hardcore.

Xeo · Mar 24, 2004, 12:29 PM

Originally posted by wataru:
So there's always liquid nitrogen for the hyperparanoid.

Sounds like more fun than heat.

f1000 · Mar 24, 2004, 12:55 PM

Originally posted by Turias:
Interesting link, although I am even more interested in reading a technical description of what f1000 was saying, before.

(Sorry, those []]][0][[[], while somewhat informative, just weren't in-depth enough for mne. I want to know about the resistors, damnit! )

Hey, I put some effort into those crappy drawings!

Turias · Mar 24, 2004, 12:56 PM

Originally posted by f1000:
Hey, I put some effort into those crappy drawings!

Don't get me wrong! I liked 'em!

I would also like a more in-depth, technical explanation, though.

There's gotta be a research paper out there somewhere...

f1000 · Mar 24, 2004, 12:58 PM

Originally posted by Xeo:
If the data on there needs to be secured even more so than that, melt the drive down, or at least break it in to parts, burn the parts, then drop each part to different locations in the ocean.

That's overkill. Just heat the magnetic films to their Curie points. Voila! Totally randomized domains.

f1000 · Mar 24, 2004, 01:02 PM

Originally posted by Turias:
Don't get me wrong! I liked 'em!

I would also like a more in-depth, technical explanation, though.

There's gotta be a research paper out there somewhere...

I drew those from my memory of an actual photo I saw when I was an undergrad, so I know that there is a paper out there somewhere.

MountainMac · Mar 24, 2004, 06:11 PM

You can even try doing this or this.

But seriously, zeroing your data will be more than secure enough; I did an 8-way random rewrite on one of my HDDs and it took about 24 hrs (b/c I'm obsessive-compulsive like that).

MM

Tomster · Mar 24, 2004, 08:18 PM

Originally posted by MountainMac:
You can even try doing this or this.

Bet that will void the warrantee.