Around one in 12 accounts on the social-networking site Facebook could be "fake", according to the internet giant's latest accounts.
It means that 83 million of the site's estimated 955 million users worldwide – or 8.7 per cent – are either not real or are breaking the company's user guidelines.
In an appendix to its second-quarter results, in which it reported only lukewarm profits and slowing growth which saw shares plunge, it said the phenomenon was more pronounced in the developing world such as Indonesia and Turkey, where it is enjoying its most rapid expansion. The situation is less pronounced in mature markets in the US and Europe.
The California-based giant has lost nearly £32bn in value since it was floated in May. Large numbers of fake accounts could undermine the site's appeal to advertisers.
Facebook said duplicate profiles accounted for 4.8 per cent of all users, while misclassified accounts – which can be business accounts wrongly labelled as those of private individuals – stood at 2.4 per cent. The company said 1.5 per cent of users were considered "undesirable", which means they breach the social network's rules and may be sending out spam or other unsolicited communications.
"These estimates are based on an internal review of a limited sample of accounts and we apply significant judgement in making this determination, such as identifying names that appear to be fake or other behaviour that appears inauthentic to the reviewers," the company said.