How did hackers infiltrate and shutdown PlayStation and Xbox?

(CNN) – Sony's PlayStation networks were still down Friday after an alleged hack on one of the busiest gaming days of the year. Xbox, meanwhile, is mostly up, but some functions are limited, according to their service websites.

What was the purpose of shutting down these gaming networks?

Cyber security expert and former vice president of worldwide internet enforcement for the Motion Picture Association of America Hemu Nigam and Forbes columnist Gordon Chang, author of "Nuclear Showdown: North Korea Takes on the World," discuss in the video above