Looks like mwave are requesting login bank login credentials when making purchases now!
https://lolware.net/2016/11/17/requesting_bank_login.html
I've shopped at here before (the amex statement credit offers), but they're no longer viable. Luckily I didn't get the prompt. Wouldn't this breaking the T&C of the bank?
This breaks more than T&Cs, it breaks every form of common sense imaginable. If something goes wrong and you gave the details away, I wouldn't presume getting compensated. This is comedy.