Charlie Card

Defcon 16, which drew an audience of 9,000 people to Las Vegas over three days, is over -- but the focus remains on a trio of Massachusetts Institute of Technology students who stole the spotlight at the world's largest hacker conference.

MIT students Zack Anderson, Alessandro Chiesa, and R.J. Ryan are still blocked from revealing how they found a way to ride the Massachusetts Bay Transportation Authority's subways free. They used weaknesses in the MBTA's Charlie Card and Charlie Ticket Fare system.