online payments and credit cards: I have questions

[cellio]

As I make the rounds doing year-end donations, I'm reminded of two things that have long puzzled me:

1. Some web sites auto-detect the type of credit card based on the number. Apparently all credit-card numbers that begin with "4" are Visa. (I don't know if the reverse is true: do all Visa numbers start with 4?) Being me, I've cycled through the other nine digits and nothing else produces a match based on a single digit. What are the patterns for other providers? And are all these sites using some standard library for this, or are programmers really coding that by hand?

2. Years ago, a three-digit code ("CCV") was added to cards to mitigate fraud. On a physical credit card, this number is stamped rather than embossed, so those old-style manual credit-card gadgets that took an imprint of your card (on actual paper, with a carbon!) couldn't record it. Um, that's fine I guess, but online, that number isn't any more secure than the card number itself. And someone who steals your physical card has the number; it's not a password. Does that number have another purpose?

Comments

[sine_nomine]

All Amex start with 3. All Visa start with four. All MasterCard start with five. All discover start with six. I don't know how they program all of this. Each credit card processing program is different. Some require the CVV, and some don't. Depending on the form that I am using at work sometimes it asks for it and sometimes it doesn't. I just always ask the donor for it. So that they don't say but last time I didn't have to give it. The form always has it it's just not always required.

[cellio]

Interesting. I wonder why forms that auto-detect Visa when I type "4" don't auto-detect the others when I type "3" or "5" or "6".

Thanks for the information.