Fake radio signals convinced a tracking system that a ghost ship followed a course that spelled out the term "PWNED." - 

Cybersecurity researchers have figured out how to get into the system used to track some 400,000 shipping vessels around the world. Since the system isn't protected, hackers could potentially use it to make ghost ships appear and even fake emergency alerts. Chester Wisniewski, of the cybersecurity firm Sophos, tells Marketplace Tech host Ben Johnson about the vulnerability.