Have a look at the guidelines for VISA password generation rules which states that your password should be of a minimum length of 8 characters, have a minimum of 1 alpha character and a minimum of 2 numbers.
As a thumb rule; one should have a master password of at least 9 which should be a combination of an uppercase and lowercase and should have one special character with at least 2 numerical characters.
This password is generally last leg authentication process while you are going to make a purchase. Check out how to make strong but easy to remember passwords for your future password generation.
