How can other information be added to my credit card?

Question

I have had cards skimmed and then used: my credit card was being declined every time I used the magnetic strip, but it worked fine when I used the chip, so I assumed that the strip had been deactivated.

I found out that my magnetic strip contained information from a completely different credit card!

Does anybody have any idea how this could have happened? I traced my steps back, and I only used it getting gas at the pump, which I don't do anymore, and once at a flea market from a vendor who used an Ipad with a device on it.

I called Capital One's fraud department, and they said it's possible for a device to not only record your information but it could actually add information to a magnetic strip; unfortunately, they no longer keep the information on magnetic-strip fraud because they don't use them anymore.

Answer 1

The magnetic strip on a card is pretty similar to the tape in a video cassette, and doesn't have any particular resistance to being wiped or rewritten, other than generally requiring a stronger magnet due to the specific composition of the material used. Given a suitable writer, therefore, it's possible to write arbitrary data to a card stripe. You can pick up a writer from online stores easily.

Most mag-stripe skimmers can pick up all the data on an inserted card easily enough - historically, they were then used to create dummy cards - so getting the data to write isn't a particular problem either.

The main question therefore is "why would an attacker write different card details onto your card?". I suppose if you wanted to muddle up the trail for investigators looking into card fraud, having multiple people generating transactions for a single card could work, but it also makes determining that it's been cloned easier (can't make in person transactions at locations 100 miles apart within 5 minutes!). Doesn't seem a great reason to me!