I think that you only need to send a radio signal, and the card chip will respond. I recall reading somewhere that there are devices that can activate the chip from 10 feet away.
I have an ID card with one of those chips in it. Our security people tell us to carry the ID cards in a RF proof sleeve to protect the data.
That's like saying someone can hack into your PC while it's turned off (and batteries removed if it has any batteries). The chip is dead as a doorknob without voltage applied from Vcc and ground. It has no battery. It doesn't even have a capacitor to hold a little power after it is pulled from the reader. Next problem is reading a chip from a distance that is outputting signal on the connectors and nothing via RF.
Furthermore a bad guy can snatch your card but can't do anything with it but use it for a transaction with a merchant. He cannot "pull" the private key or secret key and give the card back to you compromised. It can't be compromised even if you loan it to a bad guy. He can use it for normal transactions until you get it back or have it put on a stolen card list.
(1) It is dead, (2) it doesn't transmit anything even when powered, and (3) it doesn't give up secrets, it only uses them to perform the transaction that it is presented.
Evenrything I have said applies to a chip on a credit card or in a SIM card (same kind of chip). Nothing that I have said applies to an RFID chip which is designed to be powered and respond over RF. Also does not apply to a NFC device which might have its own battery and communicates over RF. The chip on a credit card should not be confused with either of those or other devices.