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The process would be easier if there was only one payment, but there must be some security or financial reason for Paypal to send you two random payments

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I suspect a 1 in 99 chance of guessing the deposit amount on a fake account using a stolen card, the odds were just too high.

There's 9801 (99 x 99) possible outcomes that anyone trying to guess the deposits would have to pick from - vs the 99 outcomes from one payment.

In order to achieve the same number of outcomes from one payment they would have to deposit anything between 0.01 and 98.01 which would be very generous of them.

But not a UX question really.

Roger Attrill
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  • I'd be happy if a vendor deposited $98.01 into my account purely for verification ;) – bangdang May 04 '12 at 15:30
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    Actually only 4900 possibilities... they could be entered in either order. But still far better than 99. – Myrddin Emrys May 04 '12 at 18:34
  • @MyrddinEmrys: who says they need to be different? – Marjan Venema May 05 '12 at 09:06
  • @MarjanVenema They don't, but that doesn't change the fact that there are 4900 possibilities, not 9801. :-) – Myrddin Emrys May 05 '12 at 17:28
  • @MyrddinEmrys: ok help me out then. Why only half? First payment has 99 possible amounts, so does the second. That boils down to 9801 possible combinations. The only way to half that number would be a constraint that the total does not exceed a dollar? But that is mentioned anywhere, so what do I miss? – Marjan Venema May 05 '12 at 19:53
  • Lets say the deposits can be 1 or 2. What I think Merlin is saying is that the deposits can be 1&1 1&2 2&1 2&2, but when you enter them at paypal, the order is irrelevant, so in the event of receiving two different payments PayPal would accept 2&1 and 1&2 as both being correct, so despite being 4 combinations, there's 3 unique answers (because 2 overlap). Extrapolate to deposits between 1 and 99, we get 1&2 and 2&1 overlapping, 1&3 and 3&1, 2&3 and 3&2, 1&4 and 4&1, 2&4 and 4&2, 3&4 and 4&3. So while there's 9801 combinations, Paypal is forgiving on 98+97+..+1 of them... – Roger Attrill May 05 '12 at 22:39
  • ... so the real total is 9801-98-97-...-1 = 9801 - (1+98)*98/2 = 9801-4851 = 4950 – Roger Attrill May 05 '12 at 22:41
  • Ahh thank you, I was a bit off. :-) I thought my math was wrong, but I couldn't remembe3r the correct formula. – Myrddin Emrys May 06 '12 at 05:04