The news has ruffled the feathers of Rupert Murdoch, head of News International which owns MySpace.
At the Lions 2008 International Advertising Festival in Cannes, Murdoch dismissed Facebook as "flavour of the month" and a mere "directory", while MySpace, he said, is a "real social networking site".
MySpace, bought by News International in 2005 for US$650m, has just undergone a redesign to de-clutter its home page.
It is still more popular in the US than Facebook, notching up 73.7 million unique visitors in May versus Facebook's 35.6 million.
Facebook has already proved more popular than its rival in the UK, having overtaken MySpace in September last year.
Facebook is estimated to be worth around $15bn, after Microsoft invested US$240m for a 1.6 percent stake in October last year.