Hard Drives and deleted files

[ReCycled]

I know when you delete a file, it's not really gone - just the address. For security issues you can buy software that will really delete your files (passwords, bank info, pin numbers, personal stuff etc) if you were selling or donating an old computer. However the other day I ran out of file space on my C-Drive and had to kill some old porn and crap to make way for new mp3's. So here's the question.
Wouldn't running up your hard drive space be another way of "cleaning" your hard drive? Let's say you had 10 gig of porn you want gone forever. Fill up your hard drive with whatever. Delete all your porn. Fill it up again with "good stuff". Wouldn't that take up the limited space that's left and replace (forever) the "bad stuff"? Then kill all the "filler" so you can resume normal operation?
 

[jägermonsta]

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[|iR|Focalor]

So the FBI found the body, huh? I told you to burn that shit!

This interests me also. I'd sure like to find some software that would allow me to hunt through my older machine for things I may want to restore. I think the drive has bad sectors on it though. The disk is 10 or 11 years old. I'm pretty sure the bad sectors is also what is preventing it from defragging 100%, it gets to about 15% and then just runs and runs and runs and never moves anything.

[reaper]

my laymen's understanding is that , you store a picture called "X" on your C partition.

the "master file table" lists all your files and where the sections of the file are stored (sometimes you can't squeeze a big file consecutively on the disk.)  then when you delete the file , the master file table is altered, and the portions of the disk that stored the file can be rewritten.  so it would not be fullproof or 100% that the file would be gone if you filled up the partition, but yeah it would be gone forever, and forensics could not recover it, if that was the only place it was stored - offsite backups, possibly in memory if it's recent and the computer wasn't shutdown...

you could just run a program that writes data to every section of the harddisk, like the *nix dd utility, which would just fill every byte on the hard drive with whatever you wanted.. non recoverable

when you format a disk , if it's a "quick format" the data will not be rewritten , i.e, it could be recoverable.  also when you repartition your disk you are just changing a partition table.

master boot record - lists of partitions

partiions - possible extended partitions

so when you partition you don't necessarily rewrite the data just the partition table

[PANTONE 7717C]

Just do a search on http://www.snapfiles.com/ for a free program or shareware.

Also the popular anti-spyware Spybot-Search&Destroy
Spybot-Search&Destroy program has an inbuilt "Secure shredder", it can be found under the Tools menu. So far I haven't been able to restore anything that I've erased with it.

[[BTF]Dizzy]

Still quite recoverable, after one pass, but essentially you're right reaper.

In simplest terms, if there was a 0 written at any particular location, and you write a 0 over that location, nothing has changed. If there was a 1 and you write a 0 it physically "looks" like something less than 1. Which means it's identifiable, too.

[reaper]

how could dd not fix it with one pass if you wrote all 1's or 0's?

I don't get it, is there some kind of physical history on the platter?

[[BTF]Dizzy]

In a nutshell, yes.  You're magnetizing some kind of ferromagnetic material with the write head when you write data. The strength of the magnetism at that location is what affects the read head. Keep in mind this is really over simplifying the process, but, by writing a 1 where a 1 already was, you haven't changed that location much at all, and by writing a 1 where there once was a 0, you've increased the magnetism at that location, but not to the same level as the previous 1 was.

(edit: It's been a long while since I read gutmann, I may have messed something up!)

[quadz]

how could dd not fix it with one pass if you wrote all 1's?

I don't get it, is there some kind of physical history on the platter?

Magnetically, yes, like Dizzy said.

Recovering information at that level is not generally available to some average Joe who is buying your computer though.  But supposedly folks like the NSA can read old data unless the drive has been wiped numerous times.

Here's some nice info describing the various levels of "secure erase" options available in Mac OS X.

http://support.apple.com/kb/TA24002

Notice the "7 pass" and "35 pass" erase use patterns specifically targeting the underlying magnetic bit encoding schemes used on the drive(s).


But anyway.... deleting the sensitive files and then filling the filesystem completely with new files containing random data, I suspect is probably good enough for, as you say, deleting some old porn and crap.


Regards,

[[BTF]Dizzy]

But anyway.... deleting the sensitive files and then filling the filesystem completely with new files containing random data, I suspect is probably good enough for, as you say, deleting some old porn and crap.

Was just about to add something similar

[reaper]

interesting, so there is some kind of magnetic history.  but apparently it would be gone after using dd x(who knows)  times.  then the NSA wouldn't be able to read the old data because it's just not there anywhere.

to bad the NSA taps into the major backbones and stores whatever the hell they want.