According to their SEC filing for the quarter ended June 30th, Facebook had a total of 955 million accounts.
Of course the primary cause of duplicates is for people who have forgotten how to access their account and created another; preferring that option to engaging with the Byzantine rules of account recovery.
Other people very deliberately have dual accounts to separate their professional life from their social life. For instance, Sophos' Graham Cluley writes "I know a primary school teacher who doesn't want her pupils to see what she gets up to socially (and the drunken pictures her friends might post of her at wild parties) and so she maintains one "professional" account (under her real name) and another "personal" account under a nickname."
This exactly the same reason school teachers maintain 'silent' telephone numbers at their residence.
The main concern however, is the staggering total of 14 million accounts used to deliberately spread undesirable content such as malware, spam, malicious links and so on.
One has to ask, if the company is so easily able to detect these accounts, why do they still exist? Surely they should have been automatically shut down upon detection.
And the same for the duplicates. If there is a clear example of an account re-created because of lost access (for instance, no updates on the old account since some time before the creation of the new account), why bother keeping it? Obviously the company needs to promote the highest-possible account count to its advertisers.
The company makes the observation, "We believe the percentage of accounts that are duplicate or false is meaningfully lower in developed markets such as the United States or Australia and higher in developing markets such as Indonesia and Turkey." They make no observation as to why this is the case, but it may depend on factors such as intermittent access to computers and possibly a more general desite to be 'obscure' in one's online dealings.
We wrote a few days ago of the dubious qualities of those who have no Facebook account, now it seems we must also be sure they we have just one! Just as long as you're not hoping to be an undercover spy!