The Magnetar Credit Card Swipe

Ned Flanders' credit card doesn't satisfy the Luhn checksum,
but could probably still be erased by a magnetar. 

Hello, Internet!  Today I'd like to talk about the Magnetar Credit Card Swipe.  Sounds like some sinister short on a derivatives deal, doesn't it?  Well, no need to worry, we don't deal with scary things like that here.  Instead, we are going to talk about a super-magnetized neutron star speeding past Earth.

A while ago I heard that a magnetar can erase all the world's credit cards from half the distance to the moon.  I did a little research and it seems like this is the go-to "fun fact" about magnetars.  Almost every time they are brought up in a popular science article, their credit card-erasing prowess is sure to get a mention.  So let's check it out!