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Secure file deletion

PostPosted: Thu May 27, 2010 2:00 pm
by Skiddie Killer
How can I delete my files securely so that they can NEVER be recovered?And if it's possible,to overwrite these areas with zeros,and not just some random content.

Re: Secure file deletion

PostPosted: Thu May 27, 2010 2:40 pm
by Goatboy
Generally speaking, 7 passes over a given file is fine. Even then, at the microscopic level they would be lucky to get a third of the information. I have a hard time believing that 35 passes is required. The guy who made that standard even said himself that it is unnecessary. A lot of tools can do this, such as CCleaner and Eraser.

Re: Secure file deletion

PostPosted: Thu May 27, 2010 2:54 pm
by Skiddie Killer
OK,thanks.

Re: Secure file deletion

PostPosted: Thu May 27, 2010 6:20 pm
by haha01haha01
Goatboy wrote:Generally speaking, 7 passes over a given file is fine. Even then, at the microscopic level they would be lucky to get a third of the information. I have a hard time believing that 35 passes is required. The guy who made that standard even said himself that it is unnecessary. A lot of tools can do this, such as CCleaner and Eraser.

7 passes is a horrible overkill. Random punks will not mess with data passed 1 time, and 3 would probably be enough to beat forensic labs. The governmental standards (DoD 5220, etc.) are extremely paranoid.

Re: Secure file deletion

PostPosted: Thu May 27, 2010 6:21 pm
by Goatboy
That may be true, but I am taking his question somewhat literally, and assuming that he was wondering how many passes it would take (practical or not) before data is totally unreadable.

Re: Secure file deletion

PostPosted: Thu May 27, 2010 8:40 pm
by 106627bg
Sorry if this is a bad place to ask, but how could data be recovered if it has been overwritten?

Re: Secure file deletion

PostPosted: Thu May 27, 2010 9:59 pm
by Goatboy
106627bg wrote:Sorry if this is a bad place to ask, but how could data be recovered if it has been overwritten?

You're in the right thread, but this thread is in the wrong forum. I'll move that after this post.

Let's say you have a file you wanna get rid of. Normally when you delete it, the data is still there, so to "securely" delete it we would overwrite it. Now for most people, a single pass gets rid of it. By most people, I mean you, me, the neighbor, etc. Taking it up one step to a forensics lab, they may be able to look at it under an electron microscope and see "beneath" the overwrite and see what the bits were like before. Taking it up yet another step from there, the NSA, or another similarly equipped agency, could see beyond several overwrites using some pretty advanced mathematical algorithms and essentially magic.

Re: Secure file deletion

PostPosted: Fri May 28, 2010 4:34 am
by Skiddie Killer
What about DBAN?Is it safe?I want to format my drive,so I thought about doing it with this tool.

Re: Secure file deletion

PostPosted: Fri May 28, 2010 12:29 pm
by Goatboy
Skiddie Killer wrote:What about DBAN?Is it safe?I want to format my drive,so I thought about doing it with this tool.

As far as I know, I think DBAN only wipes, so you'll need to format it another way. I used DBAN a few times when I sold some hard drives I got off Craigslist for free. I didn't know (or care to see) what was on them, so I wiped them just in case. It was made specifically for wiping drives, and while I haven't bothered to actually check a disk afterward, enough people have recommended it that I trust what it's doing.

Re: Secure file deletion

PostPosted: Tue Jun 01, 2010 7:45 pm
by 106627bg
Goatboy wrote:...they may be able to look at it under an electron microscope and see "beneath" the overwrite and see what the bits were like before.

Just to be sure I understand - How can you see the old polarity of a bit? Is that because the bit has only been switched on the surface and deeper in it has the old polarity? Or does the HDD not do a good enough job of flipping the bit and it partially retains the old polarity.

Thanks for helping by the way. This has been bothering my for a while.