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 83m of the site's estimated 955m users worldwide — or 8.7% — 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 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.
Facebook said duplicate profiles accounted for 4.8% of all users, while misclassified accounts — which can be business accounts wrongly labelled — stood at 2.4%. The company said 1.5% of users were considered “undesirable”, which means they breach the rules.