Facebook's latest figures show its growing number of users includes many that may come from dubious sources, such as duplicate accounts, pages for pets and those designed for spam.
Facebook members now total 955 million, but the company has admitted as many as 83 million may be dodgy.
In a quarterly filing with the American Securities & Exchange Commission, the company says there are challenges in measuring usage despite its efforts to suppress such behaviour.
Real user numbers are critical for Facebook as it seeks advertising revenues.
