Correct me if I'm wrong, but before EMV cards were introduced in the U.S., thieves would use card skimmers on ATMs and point-of-sale (POS) terminals (such as gas pumps) to steal the CVV1, which would allow them to create counterfeit cards and purchase things in stores, but they would still be unable to purchase things online, because they lacked access to the CVV2 number on the back of the card.
What I don't understand is how card shimmers work? Based on what I've read on the issue, there are three types of CVVs; CVV1, which is located on the magnetic stripe of a debit or credit card; CVV2, which is the number on the back of Visa cards; and CVV3, which is a dynamic value that's stored on the chip of EMV cards. Specifically, what kind of CVV does a card shim steal, and how can a thief make a magnetic stripe counterfeit card of an EMV card using a shim? Wouldn't the thief need access to the CVV1 located on the magnetic stripe?
Lastly, can card skimmers still steal the CVV1 of EMV cards, when, for instance, I decide to swipe the card at an old gas pump, instead of "dipping" the chip part of the card?
Edit: Just to be clear, the way this would work is, it would allow a thief to make a counterfeit magnetic stripe credit or debit card, with some special code on the magnetic stripe that would be able to fool an EMV point-of-sale terminal into forwarding the information on the counterfeit card to the card issuer, which would then decide whether or not to approve the transaction.