Morphology of credit cards

April 6, 2005 1:33 AM

I dissected my old VISA card. Underneath the hologram is a 4x4 matrix of rectangles. There are numbers or letters in each row, thus: blank, blank, '1', blank; blank, 'A', blank, blank;'C', blank, blank, blank; blank, blank, blank, '4'. Why are they there, and what do they mean?
posted by i_am_joe's_spleen to technology (15 comments total)

Yeah, because the huge unique number printed on the front of the card in raised letters is much too cumbersome for tracking…

I suspect it's some manufacturing tracking codes, like off which machine it came and on what day. Under the hologram would be the only place where it's kept out of sight, so as not to spoil the design of the card for consumers.
posted by fvw at 4:04 AM on April 6, 2005

It's intended to be a counterfeiting deterrent. Anyone with access to a plastic fabrication press and some printing materials can create a convincing enough hologram using traditional 2D trompe-l'oeil techniques. The rectangles serve as an underlying bar code, which allow officials to tell if a pile of cards captured in a raid correspond to stolen accounts from an issuing bank/agency, or if they were manufactured from scratch for use in a scam.
posted by Smart Dalek at 4:05 AM on April 6, 2005

Sounds like part of the Patriot act, some tracking mechanism..
The magnetic strip has been doing this since the late 80’s/early 90's. Every time your card is swiped; information is imported and exported onto the magnetic strip.
posted by thomcatspike at 7:27 AM on April 6, 2005

thomcatspike: do you have any resources indicating that the magnetic stripe ever has anything written to it during normal use at retail locations? Card -writers- are much more expensive than card -readers-, so I'm suspicious of this claim.
posted by odinsdream at 8:27 AM on April 6, 2005

note that there's no real point in writing to the card as a means of "tracking" you. what use would it serve? the only use case i can think of is a heuristic to catch rapid re-use of the card on high price items (perhaps a typical signature of stolen cards) when the centralised card handling system has internal delays. but, in general, writing to the card is not going to help "them" because they already have the info from the processing of each transaction. it just doesn't make sense.
posted by andrew cooke at 9:26 AM on April 6, 2005

odinsdream
You can google it a try to read through all the conspiracy crap. As a merchant years ago, the card companies told us this in training. Yes it puzzled me too until a couple of years ago.

They track your purchases and what you have spent so you don’t exceed your limits when there are delays with the merchants sending in the reports or other electronic transaction problems.
Some merchants don’t close their machines out every night and wait several days which then update your account. Bars are really bad at this, why you may see the statement date being several days later. I have one bar that it shows up weeks later. Sounds odd that they would load info onto the card itself, but that is the one logical reason I have found. That your card knows the total balance left on it.

Have you ever used your ATM card and the machine told you: you request for funds exceeds your account balance? Yet if you were to check your bank account right then, it has the funds available.
Really the ATM machine is correct because all of your banking transactions have not fully updated to the banks correct balance due to time delays in the banking computer systems. Like holidays or weekends.

From my personal experience, this happened one day. Adding, my records where wrong on my end. I then went to my bank not knowing my record keeping was wrong and the bank teller let me withdrawal the same amount of cash the ATM would not. When everything caught up in the banking system several days later, I ended up with a negative balance because the teller’s system was not fully updated. This is how I can explain that your card knows more than you think.
posted by thomcatspike at 11:13 AM on April 6, 2005

I have one bar =wish
I know one bar.....
posted by thomcatspike at 11:15 AM on April 6, 2005

There is no evidence that your card stores your balance. Card writers are not available to most people, including merchants.

The reason your online statement doesn't reflect your balance is that you are in the U.S. and the banks are cheap. They only move the data from the internal money tracking system to your online statement every X hours. Here in Canada, the system is much better integrated, and you can instantly see the debit purchases post to your online statement. I do not understand why the teller's system was not updated, that seems odd. The ATM machine is always (99.9999% of the time) right, because it talks to the real-time updated account data held by your bank.
posted by defcom1 at 11:40 AM on April 6, 2005

Card writers are not available to most people, including merchants.
Good point. So why would the merchant card reader rep tell me that information was place onto the magnetic strip when swiped?
posted by thomcatspike at 12:24 PM on April 6, 2005

"They only move the data from the internal money tracking system to your online statement every X hours."

Not true. I work for one of the major American consumer banks and all transactions are visible immediately, including those memo-posted throughout the day. This is true even for our less-than-technically-savvy main competitor Some merchant card processors may not submit transactions in real time, and those, of course, won't appear immediately.

It has nothing to do with banks "being cheap." Even cheap banks do OLTP, and most with online banking systems query the system of record directly.

"[W]hy would the merchant card reader rep tell me that information was place onto the magnetic strip when swiped?"

Because the merchant card rep had no idea what they were talking about. Card writers are neither rare nor expensive as previously claimed, but they are not included in merchant card systems because it would not be used and would add to the manufacturing cost of the reader.

The strip is a convenience factor for transaction acquisition; it's not trusted storage. Federally regulated banks can and do engage in stupid activities, but none is stupid enough to write data to a card and somehow trust that it won't be read, damaged, or altered.

In any case, as to the original question, Smart Dalek is correct: the imprint beneath the "hologram" is batch and manufacturer information. This doesn't deter counterfeiting -- nobody uses the manu coding for transactional acceptance -- so much as make it easier to identify blanks that are recovered.
posted by majick at 12:47 PM on April 6, 2005

That your card knows the total balance left on it.

majick has a much better answer, but I know this isn't really possible due to the fact that you really can't store a lot of information in the strip.

Also, how is my card going to know its balance when I make transactions relating to the account that don't require use of the card (paying my bill by check, or in the case of check cards, making deposits or withdrawals in person)? It can't. And if I used it in Canada, how would it have the exchange rate communicated back to it within the time of the swipe? Obviously, it couldn't. (And those exchange rates do change quickly. I bought two things at the same store in Germany an hour apart, and they showed up with minutely different exchange rates.)

Credit cards don't have information written to them during the course of normal transactions. They're not MetroCards.
posted by oaf at 2:04 PM on April 6, 2005

incidentally, you can store info on those cards with chips (generalising a bit - there's more than one system out there, i think). i've written code to do so. there's even a secret register that only the cia can read.
(ok, i was lying about that very last bit, but some do have dinky crypto for doing electronic cash stuff).
posted by andrew cooke at 2:51 PM on April 6, 2005

The only cards that have information written on to them are smart cards with chips on them.

Standard magnetic strips only contain very limited information, such as a name and account number. Wider strips can contain more "tracks" and thus more information, but the space is still limited.

Magnetic technology is too unstable to allow for constant writing and re-writing that would occur if the cards were written to on a daily basis. Think of how easily they can get demagnetized now, just by holding them on an anti-shoplifting desensitizer.
posted by Futurehouse at 2:51 PM on April 6, 2005

I was joking about the patriot act!!! and tracking.....
posted by lee at 9:36 PM on April 6, 2005

Have you ever used your ATM card and the machine told you: you request for funds exceeds your account balance?

Yes. This is because the merchant system is doing a pre-charge for a fixed amount, which is then voided and replaced with the real charge when the value is known. This is common in gas stations where you pay at the pump. The merchant doesn't know how much gas you're going to buy, wants to allow you to swipe the card first, but doesn't want to give you free gas. The compromise is to "test" the card for a given amount, like $20, and if that works, let you pump the gas and then void the $20 sale, replacing it with the real one.

Again, your card does not store your balance. You said it yourself, I could google it and read all the conspiracy theories, but what good is that?

Also, your salesman person didn't know what they were talking about, or genuinely didn't know how the stuff works.
posted by odinsdream at 5:09 PM on April 7, 2005