On 02-Mar-12 08:39, John Levine wrote:
Dunno why yours would have a 6 number other than that buying a range
of numbers from whoever runs 6xxx was cheaper than from Master card or
Visa.

One of the reasons for the 3/4/5/6 distinction is that, before the
advent of modern card processors, a merchant would have to decode the
card number to figure out which network to call for authorization and
submit the charge to. They could only process card types they knew and
from networks they had an existing relationship with. 4/5 cards were
easy to deal with because only the first number needed to be examined,
which is why Visa and Mastercard are so widely accepted. 3 cards are
only slightly more difficult. 6 cards, though, were generally only
accepted at the particular merchant that issued them. An ATM machine
might have only understood the particular 6 ranges used by a handful of
ATM networks.

My HSBC UK debit card used to have a 6 number (which worked in
card terminals in the US, I tried it)

Today, things are totally different. Merchants send all transactions to
the same card processor, regardless of card number, and it's up to the
processor to route it to the right network and issuing bank. It's then
up to the issuing bank to decide whether to accept a charge from the
merchant in question. Sears card, for instance, started accepting
charges from any merchant, rather than just Sears stores, and rebranded
themselves Discover. Ditto for many other 6 issuers. However, many 6
issuers still only accept charges from particular merchants for various
commercial reasons.

but they have since switched to
Visa numbers, likely so that they're usable at places in the US that
only do signature transactions.

6 numbers work just fine in the US for signature transactions; Discover
has worked that way for a long time.

Until you've bought $20 worth of tickets, it works normally, and the
ticket price is deducted from your balance when the transaction
clears. After that, the bank rejects the transaction, but if the
guard's ticket machine doesn't validate in real time, by the time that
happens you're long gone, and since the card is a bearer instrument,
they have no way to know who to go after. Repeat indefinitely until
the expiration date on the card.

Knowing the BIN ranges of debit cards and gift cards doesn't help
here, since many of them are entirely valid and the train company
will get paid.

Exactly my point.

S

--
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking