title: Are MIFARE smart cards programmable in sense I could write a program they could execute?
body: <p>Variations of <a href="http://mifare.net/products/smartcardics/mifare_ultralightc.asp" rel="nofollow noreferrer">MIFARE Ultralight</a> cards are becoming quite widespread. For example, huge transport companies employ them as payment cards.</p>
  
  <p>As I get from MIFARE site and Wikipedia there's a full-blown microcomputer inside the card - with a processor, memory, etc. When I move the card close to the reader its field induces current in the card antenna, the card computer turns on and runs some complicated protocol to communicate with the reader.</p>
  
  <p>That's all cool but could I write my own program that would run on such a card and do something useful a card doesn't do by default? What are simple examples of what such program could do?</p>