[vladvasiliu]

3dsecure works with Visa too. I don't know about AmEx, although I do know that for Point Of Sale payments we have to have a special bank contract (one for Visa / Mastercard and one for AmEx).

I suppose the merchant decides wether to use this or not by trying to find a balance between user experience and fraud risk.

In our case I think the limit is set right above the usual purchase amount (we sell movie tickets). It's low enough that a fraud wouldn't hurt us too badly and there's not much incentive for it either. Also, most of the clients don't have to fiddle with 3dsecure (in my case I would have to cary a fob around, which I never do), so it's a better experience for them.

If someone tries to buy a lot of tickets at once, they are more likely to be doing something fishy so we use 3dsecure.