>> They can't store the numbers themselves except the last four digits IIRC.)
That's not actually true. Vendors usually have to store the entire number (but not the CVV/CVN).
Most of them show you the last 4 numbers to prevent shoulder surfing and accidentally disclosing the number to someone who's taken over your accounts.
That's not actually true. Vendors usually have to store the entire number (but not the CVV/CVN). Most of them show you the last 4 numbers to prevent shoulder surfing and accidentally disclosing the number to someone who's taken over your accounts.