The GigaOM article explores how FIU SCIS Asst. Prof. Dr. Bogdan Carbunar and his team "has shown that Fitbits can be subject to attacks including denial of service, injection, and data capture." The team developed FitLock a tool to address many of the security issues.
Read more here: https://gigaom.com/2013/04/24/keeping-fitbit-safe-from-hackers-and-cheaters-with-fitlock/