Target and Nieman Marcus customers are among the tens of millions whose credit cards have been compromised in recent hacks. The news is sparking a lot of questions about American credit card security. That brings us to the next part of our series on Wall Street technology. Today we're looking at why American banks and retailers are still using the same old magnetic strip cards, instead of more secure chip and pin cards commonly used abroad. Chester Wisniewski, from the digital security firm Sophos, discusses the story with Marketplace Tech guest host Mark Garrison. Click the audio player above to listen.