Facebook says there could be as many as 83 million illegitimate accounts on its social networking website, including fake profiles and those used for spamming.

In a regulatory filing this week, the company said 8.7 per cent of its 955 million active profiles may be false or duplicate accounts.

About 4.8 per cent of worldwide Facebook profiles are duplicates belonging to already registered users, while an estimated 2.4 per cent have been labeled as “misclassified accounts” – profiles created for organizations, businesses or pets.

Under Facebook’s terms of service, pet and business profiles are only permitted to create a Page.

About 1.5 per cent of accounts have been flagged as “undesirable,” including dubious profiles used for spamming.

The figures are based on “an internal review of a limited sample of accounts,” the company said.

Reviewers “apply significant judgment” in their efforts to weed out profiles that appear to be fake, but the actual number is difficult to pin down, Facebook said.

Fake and spam accounts are a growing concern for the publicly-traded company, which relies on targeted advertising for revenue.

“We are continually seeking to improve our ability to identify duplicate or false accounts and estimate the total number of such accounts, and such estimates may be affected by improvements or changes in our methodology,” it said.  

It’s believed that fake accounts are more common in “developing markets such as Indonesia and Turkey,” the company added.

Facebook’s popularity outside North America, especially in Asian countries, has soared since the network became available worldwide in 2006.

As of June 30, there were 255 million active monthly users in Asia, compared to 186 million in U.S. and Canada combined and 246 million in Europe.

But the company has been struggling to achieve success on Wall Street since its initial public offering in May.  

Facebook shares fell below $20 for the first time Thursday, hitting a low of $19.82 before recovering to $20.12 in after-hours trading. The stock was initially valued at $38 when the company went public.

Analysts have attributed declining stock value to uncertainty over Facebook’s future growth, as well as the recent departure of several company executives.

With files from The Associated Press