Social network giant Facebook has announced that it has registered its 500 millionth member - one in 13 of the entire global population.

The site, which launched in 2004, has gained around 100 million new users in the last six months alone. Facebook said the number was "an important milestone" and added that it was "humbled and inspired" by the stories of its users.

But as the popularity of the site grows, so do concerns about privacy and online child safety - in particular bullying.

Rory Cellan-Jones reports.