Killdisk

[CypheredJ]

is it true that killdisk permanently deletes all current and previous data on a hard disk? I talked with a IT person and he said that the only way to destroy all data on hard disk is with a magnet which i knew to be true.  But Active Killdisk claims it does, so what is your opinion on it?

[Comp Guy]

I did not know it was possible for software to do such a thing. I assume the program does not run from the drive its wiping then.

[Deerpark]

Programs like Killdisk or DBAN can make it hard, close to impossible, to recover data. In any case it will make it impossible to recover the data with any software recovery solution.
But data recovery specialists may be able to recover something from hard drives with special hardware even after several wipes.
These kinds of recoveries are pretty expensive though so unless you've got trade secrets to hide wiping software should do fine.


@Comp Guy - you can wipe any hard drive on the system by loading the program completely in memory. That's how its possible.

[Comp Guy]

Programs like Killdisk or DBAN can make it hard, close to impossible, to recover data. In any case it will make it impossible to recover the data with any software recovery solution.
But data recovery specialists may be able to recover something from hard drives even after several wipes with special hardware. These kinds of recoveries are pretty expensive though so unless you've got trade secrets to hide wiping software should do fine.


@Comp Guy - programs run in memory not on hard drives. That's how its possible.

Yeah I know. I don't know why I said that

[CypheredJ]

thanks for info i just needed to know that i can be safe

[CBMatt]

Almost sounds like someone's joining the WPP.

[Flip81]

haha

[Flip81]

what about that zero fill method?  won't that delete all data?

[patio]

Zero fill is pretty effective...recovery however is still possible.
You need to keep in mind in these scenarios that we're talking about data recovery methods that can cost upwards of a few thousand $ $'s...not everyone has access to these methods...but it can be done.
The DOD ( Department of Defense ) minimum of wiping drives is at least seven zero-fill passes on each drive/partition...so take it for what it's worth.

[contrex]

No matter how many times you wipe a drive, there are methods which bypass the drive's own read/write heads. For example, on a hard drive, the data is written in tracks, circular bands of magnetic patterns representing 0's and 1s. Due to thermal expansion/contraction and tiny errors in head positioning, you can erase or overwrite the information on a track effectively enough so that the drive's own heads cannot read it any more. However, the erasure is less effective towards the edges of the track, so that a tiny band on either side of the erased track contains a 'ghost' of the erased data. You can take the drive apart in a clean room and mount the platters in a special rig with micro-adjustable read heads and over a period of time you can recover the data.

Another method involves sawing the platters apart and mounting them one at a time in a special electron microscope and scanning the magnetic material, in effect taking a photograph of the magnetic patterns. By using one or more such methods an apparently erased disk can be made to give up its secrets. It might take weeks, but it can be done.

The only sure way to delete the data is to remove the platters (which are made of a special glass) and smash them and then melt the pieces in a crucible. The CIA requires this to be done and witnessed for the most sensitive data drives it uses.

Sometimes in a court case, the very fact that a disk drive has been professionally erased can be evidence.

The level of erasure which might be appropriate depends whether we are talking about identity theft, commercial espionage, international espionage, hiding legal porn from Mom or Wifey, or hiding illegal porn or terrorist material from law enforcement or national security agencies.

[Fed]

Good stuff contrex, can you explain what happens with a CD burner?
IE: If you overwrite a file on a RRW disk does the burner 'unburn' the disk to overwrite with new data or just destroy the existing data and burn new data to a new section of the disk?
If it's the latter could you then finish up with a full disk with very little info on it due to 'overwriting', in fact 'destruction & new writing'?

I hope that makes sense to you.

[contrex]

With an RW disk the laser can heat the writable layer back into an unburnt state (the technical term is "phase change"). A quick-erase just deletes the data in the index area. Then as data is burned, the previously existing data is read. If you need to burn a 1 and there is a 0 in that place, obviously you need to do a phase change, but if there is a 1 there already, you might as well leave it there and use it again. So the same disk space can be used over and over again.

[Fed]

So that's how they do it, tricky stuff.

So do these tiny parts of the disk have 3 states?
A) Unburnt (Unrecognisable as a 1 or 0)
B) Burnt one way (Say a 0)
C) Burnt a different way (Say a 1)

I guess the same question applies to HDDs.
Unmagnetised, magnetised one way or magnetised a different way.

Sorry to bug you contrex but I like to know stuff.

[contrex]

So do these tiny parts of the disk have 3 states?
A) Unburnt (Unrecognisable as a 1 or 0)
B) Burnt one way (Say a 0)
C) Burnt a different way (Say a 1)

Two states. Unburnt=0, burnt=1.

An ordinary pressed, manufactured, CD or DVD (e.g. a music CD or a DVD movie that you buy at a shop or rent from Blockbuster) has a reflective layer and a spiral track. As the read laser is made to follow the track, it will find "pits" and "lands". The pits are actually pressed into the reflective layer, and represent 1s. The lands represent 0s.

A blank CD-R or DVD-R or DVD+R has a spiral track and uses write-once organic dye technology, this uses the laser alone to scorch a transparent organic dye (usually cyanine, phthalocyanine, or azo compound-based) to create dark spots over a reflective spiral groove. These appear like the pits on a pressed disk.

A RW disc contains a phase-change alloy recording layer composed of a phase change material, most often AgInSbTe, an alloy of silver, indium, antimony and tellurium. An infra-red laser beam is employed to selectively heat and melt, at 400 degrees (Celsius), the crystallized recording layer into an amorphous state or to anneal it at a lower temperature back to its crystalline state. The different reflectance of the resulting areas make them appear like the pits and lands of a prerecorded CD.

[patio]

Brilliant explanations contrex and Thanx ! !