Credit card breach affects Visa too

CNN’s article on the MasterCard theft hack that’s caused credit card
information for 40 million people to be compromised says that of the 40
million cards, 22 million of them are Visa cards.

Because MasterCard are the ones that went public, most articles I’ve
seen only mention them (so as a Visa cardholder, I thought I was
unaffected).  Apparently not.

How the heck do you notify 40 million people?