Hard drive erase question

Discussion in 'Mac Basics and Help' started by 204467, Aug 2, 2008.

  1. 204467 macrumors 6502a


    Jul 13, 2008
    Philadelphia, PA
    So I know that if you trash a file, using powerful enough software, you can actually recover what was thrown out. If one re-formats a drive in Disk Utility, can someone still recover what was on it using such software? I'd like to know in the eventuality that I ever sell my computer, I don't want the buyer somehow getting access to all of my stuff.
    P.S. Does anyone want to PM me a Demonoid invite code? They never seem to have regular registration open anymore.
  2. iPhil macrumors 68040



    It's slim chance if you do a 7 pass on hard drive that someone will get info...

    Even worse chance if you do 35 pass on hard drive that someone will get info...
  3. 204467 thread starter macrumors 6502a


    Jul 13, 2008
    Philadelphia, PA
    Ummm...what is a 7 pass or a 35 pass?
  4. Neil321 macrumors 68040


    Nov 6, 2007
    Britain, Avatar Created By Bartelby
    go into disk utility's click on the erase at the top your'll then see a security button, have a look
  5. Apple Ink macrumors 68000

    Apple Ink

    Mar 7, 2008
    Just insert your Install Disk and go to Disk Utility. Select you HDD and click Erase. Click 'Security Options' and choose for yourself.

    Easier way: Trash all your personal data. Click on 'File' in the finder Menubar and click 'Secure Empty Trash'!
  6. MarkMS macrumors 6502a

    Aug 30, 2006
    When you are ready to sell the computer, you will need to reinstall OS X. When you insert the OS X install disc(s), you'll have the chance to enter Disk Utility without booting into OS X. From there you highlight your hard drive and click on Security Erase Options.

    You'll have 4 options: (Actually 5 options, but I added an extra one)

    1. Don't Erase Data
    This just erases directory info. Files are still recoverable, unless they have been written over. Until the hard drive is totally filled, files are still easily recoverable. Think of it as tearing out the index in a book. You still have the other chapter pages, but you just don't know where to look if you're want some specific information. Completed in a minute or two depending on hard drive size. Takes a minute on my 200GB hard drive. ​
    2. Zero Out Data
    Writes zeros (0s) over all data on the hard drive. Good security, but it writes zeros only once. Typically done anywhere in between 30 minutes to a few hours. Takes about 45 minutes on my 200GB hard drive. I use this whenever I want to reinstall OS X for myself. Gives my MBP that fresh feeling. ​
    3. 7-Pass Erase
    Writes data over the entire hard drive seven times. This is also a standard from the Dept. of Defense (DoD 5220.22-M spec). Securely erases files on a hard drive. Expected completion time is anywhere from 8 to 24 hours. Takes about 8-9 hours on my 200GB hard drive. ​
    4. 35-Pass Erase
    Same as seven, but writes over the hard drive 35 times using the Gutmann algorithm. Extreme security. Almost impossible to recover anything from this. If you're paranoid enough, this is what you want. Expect completion time in the days. I've never done it, so I don't know how long it would take me.​
    5. Physical Destruction - Optional
    If you don't want to sell the computer with a used hard drive, your best bet is to take yours out and melt it or something. Install a fresh hard drive and install OS X. Unless you have ultra secret files or are working for the government, this isn't worth the effort.​

    That said, a 7-pass erase should be sufficient enough if you're selling a computer.
  7. flyinmac macrumors 68040


    Sep 2, 2006
    United States
    While I agree that the 7 pass method is generally sufficient, and the 35-pass pretty safe, neither are guarantees.

    No matter how many times you write over your data, the right person could retrieve it.

    The question, is are you going to sell it to that right person, or just some ordinary user who doesn't really care? Or, depending on how paranoid you are, who might that user then sell the computer to later?

    Personally, I've done both the 7-pass and the 35-pass methods on the systems I've sold more recently.

    But, if you are really concerned, then I agree that physical destruction is the only option. Unfortunately, I've heard of people recovering data from drives that have been through severe destruction methods. So, melting it into a liquid is pretty much your only guarantee. And, strangely, I do seem to recall reading something about a weakness in that method as well (though I cannot recall what the statement was).

    Here's the way I see it. If you plan on using the computer for say 3 or 5 years, then the capacity hard drive that it ships with today will be pretty cheap by then. Probably less than $50.

    So, assuming it's a computer you can open up and install a replacement drive yourself, then keeping the current drive and replacing it with an unused on at that point would be reasonable. You would spend very little, and know that they didn't have your data. And, it wouldn't cost enough to affect your profit margin much.

    Now, if it's a newer iMac. Then, it's not really something you'll want to tackle. Then you're talking about using a shop to replace the drive. And, it introduces risks of what might go wrong and what it might cost if they introduce a problem in the reassembly of the computer.

    In that case, I'd go with say wiping the drive with a 35 pass method. And, then repeat that as many times as you want to feel better.

    Odds are, no one will care enough to look. But, then someone might. And, it's only the ones with the bad intentions that are likely to care enough to look.

    I used to service computers. And, I'd stumble on stuff. But, I wouldn't use data recovery tools to go looking (unless specifically asked to). But, when someone came to me and asked me to find problems or find what was causing problems, I'd browse everywhere and report to them what I found.

    I'd often find some embarrassing stuff. And, I'd let them know what I found if I did. And, usually some teenager or husband was in trouble. Often I'd try and find a way to handle it discretely. But, sometimes a situation would present itself where I had no choice but to tell them exactly what I found and provide the options as to what they wanted me to do with it (such as when found items were the cause of the issue).

    In one case a grandmother was passing a computer down to her pre-teen grandchild and I felt she should know what was on it before giving it to said child. I handled it delicately. But, I had to tell her. I couldn't let it go to a child without giving her the option of having me remove the information / files. And, legally I couldn't just delete stuff without first asking her permission (particularly since the files in question were not part of the requested repair but rather something I accidentally located while looking for something else).

    What was always a bit interesting was when I'd be hired by a wife or mother to explore a husband's or kid's computers as thoroughly as possible to see if there was something going on. And, in the case of kids computers, the answer was almost always yes. In the case of husbands computers, it was often yes. And, it was always a little uncomfortable delivering my report. Though in many cases they were right behind me watching what I was finding. So, I only had to show them as I found it.

    I found some interesting stuff.

    Honestly, in most cases, just deleting a file is sufficient. Most people don't care beyond that. I don't. I've never gone over any of my used computers and looked for remaining data fragments. I just don't care.

    But, if someone does care enough to try, understand that no amount of over-writing the data will guarantee security. All it means is that the more thorough you are, the harder they will have to try and the better the tools they use will have to be.
  8. 204467 thread starter macrumors 6502a


    Jul 13, 2008
    Philadelphia, PA
    Heh, I was wondering if someone was going to suggest this. However, since I'm getting an iMac soon, I won't really be able to take out the drive easily; plus, if I'm selling it, I'm not very inclined to pay for a new hard drive I'm not even going to use.

    Thank you, you've been very helpful with this.

    You too have been very helpful. And if you could remember where you read that there was a weakness in just melting a drive, could you please PM me a link, or just start a thread about it? That sounds really interesting.

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