"trace" magnetism on USB drives

[ChrisGreaves]

I remember reading, years ago, that hard drives, the sort that spin at 3600rpm, could be un-formatted by using equipment that could sense weak traces of the strong magnetic signal that was on the platter before the disk was reformatted.
I don't know if this is true or not; it is probably only serious if you are a techie with the CIA.

Recommended procedures were to fully-format a hard drive at least three times before releasing the drive.

This may just have been the equivalent of sending a rookie aviator for "a bucket of propwash".

Question: If it were so, would it still apply to a hard drive of the USB type, sometimes called a memory-key or a thumb-drive?

[StuartR]

It certainly is true, and even three formats is not sufficient. That is why some companies make good money selling hard drive shredders!

The issues with a thumb-drive are slightly different. They change the mapping of physical memory to logical disk sector to spread out the usage across the memory, and this means that deleting and over-writing a file may just change some pointers without over-writing the actual data.

My preferred approach is to encrypt all data on all hard drives, that way you are at much lower risk of someone getting your data if they get your physical drive.

[HansV]

In addition to Stuart's reply:

The usual method of securely erasing a disk (overwriting the entire disk with 0s or with random data multiple times) may not be a good idea for flash disks - it may shorten their lifespan.
USB sticks are cheap, so if you want to be secure, use a hammer to destroy them physically...

[PaulB]

Or you could freeze the USB stick and try to pass it off as a strawberry...

[Jay Freedman]

http://oithelp.nd.edu/information-secur ... b-devices/ and http://gizmodo.com/5489933/leave-no-tra ... umb-drives suggest a couple of programs that work with USB sticks. Programs that are intended for spinning hard drives may not work well with USB sticks because of the difference in internal architecture.

Also of interest: http://gizmodo.com/5773105/dry-cleaners ... es-in-2010

[Claude]

My understanding of how formatting works is that formatting simply checks the entire disk for errors, if an error is found, that sector is marked as bad, when formatting is complete, the MBR is updated to show all sectors free (except the bad ones) and no data is actually removed.

This may of course have changed over the years.

My way of ensuring that absolutely none of the data is recoverable is to use one of these tools which should also work on a USB / flash drive, although they were invented before USB drives.

[Rudi]

Or you could freeze the USB stick and try to pass it off as a strawberry...

An alternative to Pauls security method is:

To use a strawberry USB...

Lovely-Strawberry-shape-USB.jpg

...and have it freeze the PC when you plug it in...

2013-07-31_06h35_09.jpg

[Claude]

Or you could freeze the USB stick and try to pass it off as a strawberry...

Now now Paul, Chris doesn't refer to any berries in this thread, I think you're confused.

[HansV]

An alternative to Pauls security method is:

To use a strawberry USB...

Isn't that an unfrozen blackberry?

Also see: My blackberry is not working.

[Argus]

As Hans says, it's flash memory, so it is relevant for a range of storage devices; memory cards, SSDs etc.; hence the differences mentioned by Stuart, (and no magnetism).
(And USB is a standard that defines all things needed to connect and communicate with a range of devices. There are plenty of external mechanical drives using USB. But yes, some of these flash memories are called something along the lines of USB-... here as well, though not hard drive, unless it’s a SSD ).

Given peoples curiosity (it doesn't matter if it says "contains the mother of all viruses" on the outside, most people will plug one in if the they find one), it is a good idea to encrypt or destroy it before you mislay it, though the latter might be difficult.

[ChrisGreaves]

My preferred approach is to encrypt all data on all hard drives, ...

Thanks Stuart, I agree.
Right now the laptop is partitioned into an unprotected C and a protected D, the D is in fact a TrueCrypt volume, so the theory is/was that all my private stuff was protected, but I'll be rebuilding Windows soon, and I have a mind to have the entire drive protected.
This because I realise that my user settings sit on drive C.

I must reread TrueCrypt's excellent user guide first.

[ChrisGreaves]

...use a hammer to destroy them physically...

That sounds better than my current method of getting rid of my data, which consists, in the main, of leaving them lying on the table in the public library and heading off home.

What I need at my age is a Virtual USB drive.