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Erase my mac completely

J

jmufellow

macrumors regular
Original poster
Jun 17, 2005
215
0
I am selling an old mac and wanted to erase everything before I sell it. I asked a similar question about what I should do when I sell it and was told to boot from the os x dvd and do a secure erase (zeroing all data). Then afterwards do an erase and install.

Will this effectively erase my system so no bits of info are left lingering on it? I just want to be safe before I let it go in the wild. what is the benefit of programs that supposedly securely erase a drive is os x can do it on it's own. Thanks
 
Zeroing the data means that new (random) data is written to all sectors of the hard drive, overwriting your old data. If you don't zero the data then your old data isn't overwritten (or replaced) until necessary. In other words, it stays there until that space is needed for other new data.

There are apps that can find "deleted" data that hasn't been zeroed but there's very little that can be done to find data that has been zeroed over. In theory, it's actually nearly impossible. If you're really serious about getting rid of all traces of your old accounts, zeroing the data before reinstalling the OS really should be enough. In most cases the zeroing isn't necessary though IMO. :)
 
Thanks Madjew, no one is smarter than you! Well ok, maybe there are a few other smart ones on this board. :)
 
jmufellow said:
Thanks Madjew, no one is smarter than you! Well ok, maybe there are a few other smart ones on this board. :)
Click to expand...

He's so smart, he's positively mad.




And I agree with him 100% I started zeroing the data on my mac before I got rid of it. It was taking forever! (as was everything. Hence, the reason I was upgrading). I gave up halfway through and sold it as is. Nobody has stolen my identity. They might have some old erotic pictures though.....hmmm
 
maya said:
Zero-Data, with a 35 time pass. ;) :D


It would take 35 times the effort to retrieve any data if possible. :D
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well I'm not that paranoid. it's a 160GB drive, it would take forever. I think one pass will satisfy my paranoia. :)
 
jmufellow said:
well I'm not that paranoid. it's a 160GB drive, it would take forever. I think one pass will satisfy my paranoia. :)
Click to expand...

Can you blame me, I would with data recovery and security. One pass is not enough if you have some "sensitive" data on there. ;) :)

That one pass can be broken in about 30m - hour, depending on HD and system recovery hardware. ;) :)
 
It depends on how serious they are. Aside from physically destroying the disk, in theory it's always possible to recover. But secure erase does make it more difficult. :)
 
I would do the 7 passes. It should make anything that was on the drive unrecoverable. Zeroing the drive is still recoverable sometimes, depending on how much the person you are selling the Mac to wants to spend to find the info. 35 is for the paranoid, sensitive data companies out there that need to know that everything is gone and no chance of recovery.
 
dogbone said:
Could someone explain how it is that overwriting the date does not make it unrecoverable?
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The very simplified answer:

Each bit (0 or 1) on a hard drive is made of a set of magnetic particles that, when induced by electric current will align themselves in a | or – pattern, indicating a 1 or 0. The only thing is that not all of the particles will line up perfectly, so given good enough scanning equipment (and some security firms and government agencies have very good equipment), you can figure out which states each bit has been in before.

So since zeroing out all data just sets all those bits to 0, it's fairly easy, with the right equipment, to reconstruct the HD. With 7 pass random, or even 35 pass random the job gets harder, but still not impossible, though in most cases the cost of reconstructing the data will (especially with 35 passes) far surpass the value of the data. So for most regular users zeroing or, if you're a bit paranoid about your data, running the 7 pass, should be more than good enough.

But, for the most sensitive data of all, e.g. corporate or state secrets, no formatting, no matter how deep, will completely erase everything, and this is why most data security firms offer a secure destruction of old HDs, where they physically completely destroy the magnetic disks inside the HDs.
 
Mitthrawnuruodo said:
But, for the most sensitive data of all, e.g. corporate or state secrets, no formatting, no matter how deep, will completely erase everything, and this is why most data security firms offer a secure destruction of old HDs, where they physically completely destroy the magnetic disks inside the HDs.
Click to expand...

Its also been rumored that government agencies with top secret information (NSA, CIA, FBI) do not discard the destroyed disks (which are sand-like in properties) but rather, they store them in warehouses... :cool:
 
Tiger has the securely wipe free space option. Me being a spaz decided to do that to my hard drive selecting the 35 time zero option on the 50gb of free space my computer had. The process took a solid 72 hours! So make sure you have lots of time schdeduled for such a task.
 
Mitthrawnuruodo said:
The very simplified answer:


But, for the most sensitive data of all, e.g. corporate or state secrets, no formatting, no matter how deep, will completely erase everything, and this is why most data security firms offer a secure destruction of old HDs, where they physically completely destroy the magnetic disks inside the HDs.
Click to expand...

Thanks for that explanation, I've always wondered. Regarding the above why send the HD to a security firm for destruction, wouldn't a sledge hammer do the trick?
 
dogbone said:
Thanks for that explanation, I've always wondered. Regarding the above why send the HD to a security firm for destruction, wouldn't a sledge hammer do the trick?
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For all practical purposes, yes. Once the HD is deformed, pickup is broken and air flows in to the vacuum that the disk lie in the HD is dead. So unless you have really valuable data, reconstructing them would just not be profitable, for you or a potential data thief.

But the most paranoid will take out the magnetic discs and ground them up into sand/flour, and as jdechko indicates maybe even store that to avoid it falling into the wrong hands. Because if you get hold of the physical disks, and have the above mentioned equipment, you still would be able to pull some data off it, no matter how damaged it is.

(Not sure you'd actually get something off disk grounded up into flour, but I guess certain government agencies are more than averagely paranoid, and also have to consider the possibility that the recovery procedure might get improved in the future and be able to get some info out disks that look beyond recovery now.)
 
this is funah said:
i have a g3 ibook i want to do a software restore (erase everything, start anew).... is there a place where i can find the procedure?
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It's actually quite easy:

- Backup all your data! Everything on the iBook will be wiped.

- Insert the first Software Restore disk that came with your iBook, or (if you've bought a later version of OS X) the first Panther (10.3) disk or Tiger (10.4) DVD, and run it.

- Follow instructions on screen, choose Erase and Install. And your HD will be reformatted and only the original configuration/system will be installed.
 
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