Facebook founder Mark Zuckerberg announced last night that the social network now has over 350 million users around the world.

The number indicates continued strong growth, because just in September, Facebook announced that it has surpassed 300 million. In early November, it was reported that Facebook had reached at least 325 million. Zuckerberg announced the news in an open letter, which was made available on the company blog, and linked to from a prominent spot on users Facebook homepage. The letter was not written simply to brag about the impressive number, however.