What's inside WhatsApp?

Available for over a year

The inside track on WhatsApp, the startup bought by FaceBook for $19bn. How phone maker Xiaomi has big plans beyond China. And is it time for business to challenge bogus reviews? Rory Cellan-Jones was joined in the Tech Tent by the editor of Wired UK David Rowan, and BBC Technology Desk members Carolyn Rice and Mark Ward.