Member
Join Date: Feb 2006
Location: Orlando
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So after 4 months with my MBP and over a dozen calls to Apple help, they have decided my MBP is a lemon. They want me to send it in so they can swap out the logic board, hard drive, super drive, and the battery that is swollen and cracking from the extreme heat (causing the computer to die after 2 minutes without an a/c adapter).
I transferred all my data and booted off an external drive in order to use disk utilities to wipe the drive. In disk utilities I have an option to "zero all data" or do a "7 time zero" or even a "35 time zero". This is my question... Is 7 or 35 time zero that much safer? I thought once it was written over once it was all gone. Is it really worth it to do a 7 or 35 time write over or will that just wear out the drive sooner? How many times must it be wiped for it to be gone for good? |
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Sneaky Punk
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Unless you have something you are really worried about one zero over should be enough.
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Student extraordinaire
Join Date: May 2004
Location: Canberra, Australia
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Zero all data will stop ordinary users from retrieving the data (that is, it won't be recoverable with any software). It will still be retrievable by specialist data-retrieval places (that is, it will be recoverable with special hardware).
To stop that, you'll need to use 7-pass overwrite (35-pass is silly overkill). Myself, I used to use 7-pass. Now I just all-zero drives. The sky was deep black; Jesus still loved me. I started down the alley, wailing in a ragged bass. |
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Member
Join Date: Feb 2006
Location: Orlando
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Thanks for the info. I did a 7 times pass and I'm sending it in. I was just curious as to how many times it takes to wipe it beyond recovery or is there something crazy that could recover it no matter what. The 35 times pass seemed like an overkill, but then again, why offer it if it was not needed for some reason.
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I shot the sherrif.
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I overwrite my drives 99 times then shred them. Then I pee on the scraps and light the whole mess on fire with a quarter gallon of gas.
YMMV. |
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Member
Join Date: Feb 2006
Location: Orlando
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anyway... what hardware can recover after 7 times? any good links I can read up on? |
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I shot the sherrif.
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Unless you're worried about the CIA, or you have an arch enemy at OnTrack who might get their hands on your drive, a 7x wipe will be fine. Your porn will never see the light of day again.
Google is your frenemy. Caveat Emptor - Latin for tough titty I tend to interpret things in the way that's most hilarious to me |
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Member
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i Believe, that if life gives you lemons, you should make lemonade. And try to find somebody who's life gives them vodka, and have a party! |
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Member
Join Date: Feb 2006
Location: Orlando
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Senior Member
Join Date: Nov 2004
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If you aren't doing anything illegal, storing the codes to authorize nuclear launches or whacked-out spy-novel stuff, a single write to zero's will obfuscate your data well enough. Only the folks interested in the previous stuff have enough compute power to even consider trying to read between tracks on peviously unknown data, and even they are only interested in very specific drives. The fact you are posting about this shows your drive isn't on their list, relax! |
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Student extraordinaire
Join Date: May 2004
Location: Canberra, Australia
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Thanks for the insight, Enki.
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is the next Chiquita
Join Date: Feb 2005
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Would it be quicker to insert a hard drive in a capactitor bank capable of generating 10 tesla and flip the switch?
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owner for sale by house
Join Date: Apr 2005
Location: Charlotte, NC
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Sure, but that would probably mechanically destroy the harddisk.
There's really no reason to be overly paranoid. For normal data, zeroing once is more than sufficient (lest somebody at Apple have a lot of time to sift through deleted data on harddisk that gets sent in). If you have really valuable data, or data that could put people at risk if it got into the wrong hands (like the names and addresses of hundreds of thousands of people serving in the military and their relatives, say), zeroing seven times removes any traces of the data for practical purposes. Sure, if you were to go after the disk with an electron microscope, you might in theory still be able to pick out the odd bit. But in practice, it's simply impossible. Getting access to interesting data is much easier through social engineering or carelessness than using some supposed high-tech recovery methods. |
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FYI, it is often standard support procedure to replace hard drives regardless. So even if they were to send you back the same MacBook Pro, they'll probably put a new hard drive in first and refurbish (presumably including a thorough data wipe) your previous one.
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is the next Chiquita
Join Date: Feb 2005
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owner for sale by house
Join Date: Apr 2005
Location: Charlotte, NC
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How do I know you're not working in some research lab, or have access to an MRI?
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is the next Chiquita
Join Date: Feb 2005
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Oh, sure!
"Hey, after we're done with Ms. Green scan, I've got this hard drive I want to wipe" "All right! I love to see one of those babies fry in this MRI!" "Yeah! Ain't working at MRI loads of fun!" "Word, dude!" |
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I shot the sherrif.
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Actually, we have access to such hardware at my work in the magnetic research areas. We use it to destroy HD data regularly, so it's a somewhat legit concern.
Google is your frenemy. Caveat Emptor - Latin for tough titty I tend to interpret things in the way that's most hilarious to me |
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is the next Chiquita
Join Date: Feb 2005
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But just wait until the next patient comes in and ask what is this smell in MRI room.
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Veteran Member
Join Date: Oct 2005
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Veteran Member
Join Date: May 2004
Location: Clayton, NC
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Anyway, we used to do fun things in the MRI room. Well, actually, it gets boring pretty fast. I remember coat hangers... and, um, hmmm. One time the director took an unloaded gun in the room to see if the field would pull the trigger (it did!). Never tried to wipe a drive, though. Ugh. |
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owner for sale by house
Join Date: Apr 2005
Location: Charlotte, NC
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Ah, the fun you can have with just a few millions worth of highly sensitive medical equipment ...
I've never been near an MRI, but I worked for a radio station for some time. They had this "device" the size of a fridge for erasing reel tapes that seemed to consist of a large magnet that would be dropped when you pushed the button (after inserting the tape roll into a slot). There were warning signs all around it not to go near it with a credit card or floppy disk ... that thing may not have created anything close to 10T, but it probably would have been plenty to thoroughly erase a harddisk. |
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Banging the Bottom End
Join Date: Jun 2004
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You don't need specialized hardware either. There are military programs with data detection algorithms that will extract data from zeroed drives. This is why the DoD sets a standard for data elimination, which happens to be 35 passes of cryptographically random data. 35 passes of the same data will leave pockets of old information stored on the hard drive simply because one bit != one magnetic particle on the hard drive. One bit of information is stored in a cluster of magnetic particles. If you try to write zeroes over and over again, the hard drive won't wipe out the entire cluster of particles because if the whole hard drive read zero then it would be very difficult to tell one sector from another. Last edited by bassplayinMacFiend : 2006-06-28 at 15:50. |
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Now in lower-case™!
Join Date: Feb 2006
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Senior Member
Join Date: Nov 2004
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The 35 passes BS was all developed based on the 27 zeroing passes necessary to statistically "erase" the drive as claimed by the gent that used the known contents drive in the first place. He claimed he needed 27 passes to not find any recognizable trace of his pre-known data in known locations on his control drive. The drives used at the time the research was done were very old technology compared to today's drives. Head movements are on the order of 100x finer now than they were 5-7 yerars ago when this nonsense was first published. The head positioning sloppiness over the previously wide inter-cylinder spacing is what supposedly required all the extra writes, now those physical issues are pretty much a thing of the past, making the 27+ overwrites even more ludicrous. Yes, the ultra paranoid standard necessary for a very small number of drives may say 35 passes, but that crap is written by knuckleheads that can't even figure out how to use Word to create a table of contents or how to use tabs instead of a bizillion spaces! The paranoid non-technical supervisors hear some ya-hoo showed off something at a security conference and then have some other non-technically adept ya-hoo write an instruction to surpass the worst case estimates, regardless of whether there is any real technical need or not. I used to work with knuckleheads like that every day. Last edited by Enki : 2006-06-28 at 15:59. |
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owner for sale by house
Join Date: Apr 2005
Location: Charlotte, NC
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I shot the sherrif.
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Actually, most sensitive data is required to be shredded now. Erased isn't good enough.
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Senior Member
Join Date: Nov 2004
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True enough. But that has more to do with humans who screw up and don't actually erase anything but think they do. On the flip side of that, even an idiot can physically destroy or shred something enough to render it's data unretruevable.
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