Securely disposing of CD/DVD media (while maintaining maximum laziness)

December 20, 2007 10:29 AM

Securely disposing of CD/DVD media (while maintaining maximum laziness)

Recently, I've seen a slew of CD/DVD media shredders for sale. I think that having one of these is overkill unless you have many CD/DVDs that need to be securely disposed of.

My method of disposing is very simple and requires very little effort: scissors. Just one cut half way in is all it takes. Here's my theory on why this works:

* The recordable layers of dye or material get distorted even beyond the cut, thus increasing the damage
* Unless it is glued back together, the disc is warped slightly
* By nature, discs are read in a spiral motion. So if that "data spiral" is interrupted, it would be difficult for the average CD/DVD reader to compensate even with error correction (since the error corrected areas are also damaged).

Or would it? Do they have machines that can selectively read CD/DVDs even if the physical structure is warped/distorted/broken? Let's say you only have half a DVD?

posted by colecovizion to Technology (26 answers total)

Forensics people can do crazy stuff. I've heard of data recovery happening on hard drives recovered from the smoldering wreckage of a burnt down building. That being said, unless you are designing nuclear weapons for the pope I can't imagine anyone working hard enough to get the data off of a cd/dvd you cut in half. It would require a lot of effort to read it.
posted by zennoshinjou at 10:36 AM on December 20, 2007

I have a discman that will play a cd that is missing 1/3 of the pie. It will play until it hits the gap. I have to imagine for data recovery one could get around that, and get parts of the data. I think just about any data one has would justify a shredder. they aren't that expensive.
posted by Amby72 at 10:39 AM on December 20, 2007

depends who is trying to read it. the script kiddie next door wouldn't be able to do much, the NSA could extract almost every intact bit. it would cost a lot, and your data would have to be seemingly rather important, but if they wanted to, they damn well could.

i bet even a really high res scan could work, at least for CDs. DVDs have data pits that are (i think) an order of magnitude smaller, needing much greater resolution to be useful.

i use the microwave. put a half a dozen or so on a paper towel, give them 15 seconds, zappo! pretty light show, bad smell, very compromised data. yes, the NSA could get 30% or so of the data back but then i break it into pieces and mix it with the used kitty litter.

combined with the fact that there's absolutely no real reason anyone would want this data (mostly 10 year old downloads of system utilities etc) i sleep well at night.

shredders work, especially if you already have one for your junk mail
posted by KenManiac at 10:40 AM on December 20, 2007

If someone is so determined to get your data that they'll go to any amount of trouble then even one of those shredders won't help you.

If they're just looking for anyone's personal info (e.g. for identity theft) and aren't interested in you in particular, then they'll just get whoever's info is easiest to access and cutting the CD will be sufficient.
posted by winston at 10:44 AM on December 20, 2007

Bruce Schneier once recommended popping them in the microwave for a few seconds. I've tried it and it seems to crack/burn the internal metallic-foil layer into a million little pieces. I'm still not 100% sure that someone with a lot of time and an electron microscope couldn't retrieve the data, but it vastly increases the effort required to recover the data with minimal effort on your part. It certainly strikes me as more secure than just cutting or breaking it into two parts, although it may not be as effective as a purpose-built media shredder.

You might want to do it in an old microwave, though... and don't do it for more than a second or two; it doesn't take long.
posted by Kadin2048 at 10:46 AM on December 20, 2007

My coworker always takes a cd/dvd and scrapes it on our cement floor a few times before he throws them away. This probably doesn't penetrate through the metal, so if someone wants to get to the data, I suppose they still could. Maybe if you put it under your foot and scrape for a good while, you could get through the plastic and scratch the hell out of the metal, and I would imagine that would completely prevent anyone from ever retrieving the data.

Alternately, you could microwave them.
posted by kpmcguire at 10:49 AM on December 20, 2007

Two words:
Belt Sander
posted by notbuddha at 10:55 AM on December 20, 2007

When I was at university our head of (electronic engineering) department liked to show off just how good the error correction is on CDs (he'd put a 1mm mask across a disk radially). The data is interleaved and the error correction is quite extensive, so if you have just one or two slices in the CD, it probably makes no difference at all in reading the data. The only 'tricky' part would be lining up the two parts successfully.

I'd second Bruce Schneier's recommended method - you're causing all sorts of defamation of the data layer of the disc, and it's quick (and possibly quite pretty). You may enjoy throwing the microwaved media through a shredder too.
posted by lowlife at 11:03 AM on December 20, 2007

Nthing microwave. Don't forget to recycle your discs after they're burnt: you don't want that aluminum or gold layer going to waste.
posted by infinitewindow at 11:25 AM on December 20, 2007

Yes, the ol' horno microondas treatment.

But heed my warning--it stink-stinkity-stanks. Out of curiosity, I nuked a CD after hours at my job of work a number of years ago, and I was really glad I was the only one there at the time, and doubly glad I did not do it at home.
posted by Admiral Haddock at 11:34 AM on December 20, 2007

Microwave is the way to go. But the it will create some nasty, quite toxis smoke. You won't need another microwave (what would be an option) but you could just put the CDs into a sealable plastic container. A container like a lunch box but one that really closes tight. Of course you won't use this container for food afterwards. I've tried sealable Zip-log bags but there will be some sparking, the bags won't withstand that. Hence you need a plastic container. Open it outside your building/house, trash the CDs/DVDs, keep teh container for reuse for CD disposal.
posted by yoyo_nyc at 12:08 PM on December 20, 2007

PS: I don't know how many CD you are going to trash but I would recommend 5 CDs at a time, 10 seconds in the microwave.
posted by yoyo_nyc at 12:09 PM on December 20, 2007

Why not just burn them? Pretty coloured flames!
posted by meehawl at 12:13 PM on December 20, 2007

zennoshinjou: I've heard of data recovery happening on hard drives recovered from the smoldering wreckage of a burnt down building.

That isn't necissarily anything special at all. I'm sure people have recovered hard drives from smoldering wreckage, pluged them into a PC, and found them working fine. We are talking about a metal box inside another metal box, after all.

KenManiac: i bet even a really high res scan could work

No chance:

Each pit is approximately 100 nm deep by 500 nm wide, and varies from 850 nm to 3.5 μm in length.

The dot size at 2400dpi is about 10μm. On top of that, there is the conversion from polar to cartesian coordinates, and there is aliasing. For practical purposes, 2400dpi is about two orders of magnitude short.

lowlife: just how good the error correction is on CDs (he'd put a 1mm mask across a disk radially).

Did the demonstration involve music or data? As Amby72 observes, the music standard is designed to play through errors.


Honestly, you have to reconsider what you are worrying about.. Just putting old CDs into the nastiest kitchen garbage will dissuade all but the most determined adversaries. Beyond that.. A cut sounds fine.. I'd consider a brutal scraping with a scratch awl, or the tip of a box cutter, because it seems easier than cutting through the tough plastic.
posted by Chuckles at 12:15 PM on December 20, 2007

Uh, for all of you worrying about the metal, you know that's not where the data are stored, correct?
posted by klangklangston at 12:23 PM on December 20, 2007

Scrapping the painted side, that is. Also, that applies to CDs only. DVD data is often sandwiched in the middle.

Which brings up something I deleted previously: If wrong few bites end up on the wrong piece of shredded disc, you lose no matter what you do.

Best to just dial down the fear a little. And, if security really matters, use encryption.
posted by Chuckles at 12:24 PM on December 20, 2007

I have a heat tool for crafting and I've shot some CD's with it*. Makes them bendy and warped not to mention easier to cut with scissors.

* also have dunked the warped pieces in glue and micro glitter but I have strange ideas about fun
posted by pointystick at 12:28 PM on December 20, 2007

When I cut things in half to dispose of them, I deposit each half in different trash bags. When I'm feeling really anal retentive I'll take them to the curb different weeks.

Except now I have a paper shredder that also does CDs and credit cards, so it's no longer necessary.
posted by iguanapolitico at 12:36 PM on December 20, 2007

Here's the rule for secure disposal: When you've made it more expensive to recover the data than would potentially be gained by actually performing a recovery, you're secure. So, it all depends on the data, really. My guess - unless you're destroying a draft business plan for the next Google, cut the CD into 4 pieces, and you're good.
posted by deadmessenger at 12:54 PM on December 20, 2007

Because it's been mentioned here I'll just note that extracting overwritten zeros and ones from an HDD is almost certainly a myth.
posted by holloway at 12:57 PM on December 20, 2007

Response by poster: Very interesting feedback!

It appears that most people are in favor of the microwave, however, I'm still not convinced that my method isn't effective. I can't even properly seat the CD into a reading device the way I do it, which makes it difficult to read. But then again, maybe the error correction is that good.

Does anyone know more about these "secret" readers?
posted by colecovizion at 2:46 PM on December 20, 2007

For the record, putting metal in your microwave isn't dangerous at all and it won't cause your wave to explode. For lots of fun, take two pieces of aluminum foil and fold them into z's...or rather a big long piece of z's and put them about 1cm apart. Nuke.

The plasma arc will travel up and down the ladder, it's pretty cool.
posted by TomMelee at 3:58 PM on December 20, 2007

Sander is where it's at. Once you're done, the CD is just a bit of polycarbonate and your pants will look like a disco ball. Can't really get much more entropy than that without burning the dust, and it's entropy you need.

Cutting will defeat people using just a CD drive but not someone with the technology and determination; after all, all the data is still sitting there undamaged. All you've done is made it difficult to put in a drive.
posted by polyglot at 4:50 PM on December 20, 2007

a reminder - if you're going to use physically abrasive means, either a sander or doing the twist on concrete, the top, eyeball side is the one to work on. it's much thinner than the bottom, laser side.

it's usually only varnish and paint, vs polycarbonate (tough stuff indeed)
posted by KenManiac at 7:21 PM on December 20, 2007

Cheaper than potential damage to your microwave (read the instructions. They'll tell you, something must be inside to absorb the energy, or it feeds back and fries that magnetron) is a simple toaster. Toast the CDs until they warp. Watch carefully, lest you start a fire!
posted by Goofyy at 6:42 AM on December 21, 2007

colecovizion, the answer really depends on what you are defending against. Are there people who would be highly motivated to read this particular CD? Then I'm not sure any of the methods here are foolproof. Or are you just defending against identity theft in general? Then I think any of them of them (including yours) are acceptable.
posted by winston at 12:27 PM on December 23, 2007