Rory Cellan-Jones tells the story of the social networking scramble of the early 2000s and finds out how Facebook emerged to become world’s biggest social network. Facebook wasn’t the first site of its kind - other businesses had a lot in common with Mark Zuckerberg’s efforts - but its simplicity and the single-minded focus of its CEO gave it an advantage over the competition. With big growth has come big controversy, over privacy, security, and targeted advertising. Rory finds out that some people are becoming more wary about what they share online - could new networks spot a gap in the market and steal Facebook’s crown? Part 2 of 3.