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Comment by jedberg | Hacker News Reader

I know that. I've talked with people who work on banking systems who have confirmed it.

It's true there are other reasons for the limits, such as the ones you listed, but if you are with say Bank of America, your limit and my limit can be different. The more credit history you've built up with the bank, the higher the limit will be. This is mostly because they trust you more and therefore consider the risk for defrauding smaller.

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It takes a fraction of a second to send the withdrawal to the main office - how would a scam based on this really work? A second card with another person at a different ATM? Even then, you'd think you could serialise per-account without affecting throughput at all.

> It takes a fraction of a second

99.999% of the time? It's impossible to guarantee that 100% of the time.

And it would still be acceptable to wait 0.001% of the time, would it not? Or degrade to limit mode in that situation?

I'm not sure but I've seen Visa terminals that behave as if they enter some kind of offline mode when their ancient GPRS connection in the middle of the woods time out. In this mode you can only do smaller purchases and they are then later sent to the bank once the store gets a connection. This is for Visa debit btw, not credit.

Sure, a fail-safe mode makes complete sense. I'm just doubtful that there's a need to be in this mode 100% of the time.

Here is a news article from 2013 about such a scam:

http://www.nytimes.com/2013/05/10/nyregion/eight-charged-in-...

There's not really enough detail here to support either point of view. There's hacking & skimming in addition to hitting withdrawal limits. It's arguable form the article's information that implicitly trusting up to the withdrawal limit was partly to blame. I'd prefer to see some evidence that it's necessary to put this trust in place at all.

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