Facebook is more popular than porn. That's according to a senior manager at web ratings firm Hitwise.

Bill Tancer, general manger of global research at Hitwise, says that out of the 172 web categories tracked by Hitwise, social networking is now top dog among 18 to 24-year-olds.

Next up: social porn?

"I've actually been puzzled by the decrease in visits to the Adult Entertainment category over the last two years," says Tancer, writing for Time.com. "Visits to porn sites have dropped from 16.9 per cent of all site visits in the US in October 2005 to 11.9 per cent as of last week."

That, ladies and gentlemen, represents a staggering 33 per cent share. Of course, this doesn't actually take into account that there might actually be more visits to websites in total. But Tancer says the upturn in social networking might really be related to the downturn in porn.

"If you chart the rate of visits to social-networking sites against those to adult sites over the last two years, there appears to be a strong negative correlation."

However, for surfers over 25, so-called 'adult entertainment' still rates second after search engines.