Can the data be easily intercepted when (or after) the card is swiped? My main concern is at a trusted vendor. There are two possibly different situations:
1) a typical point of sale scanner with a land line or internet connection
2) a standard reader on a smart phone, using the supplied software
Does the typical system usually store the credit card number or does it merely transmit it to the verification center? Are these transmissions encrypted?
edit: I am only concerned with mag strip readers and client side security (server security is a whole different issue). I didn't mention camera or shoulder surfing as concerns because those threats are always a possiblity. How secure is my card number and PIN after they are entered into the device?