According to company filings this week, Facebook has revealed that 8.7% of its 955 million active users might not be real.

The estimate has been introduced at an unlikely time when advertisers and investors are concerned with Facebook's IPO's and the marketing on the network.

Facebook categorized the 83 million in three groups. Fake users, duplicates, and undesirables which were profiles deemed to be in breach of Facebook's terms of service, meaning profiles which have been used for sending out spam messages or other content.

"We generate a substantial majority of our revenue from advertising." The company said in the filing. "The loss of advertisers or reduction in spending by advertisers with Facebook could seriously harm our business."

A Fake company called VirtualBagel was set up to investigate allegations of fake "likes" by BBC's technology correspondent Rory Cellan-Jones, last month.

His investigation discovered that the large majority of "likes" for the fake firm originated from the Middle East and Asia.

To make matters worse for Facebook, last week, digital distribution firm Limited Press alleged that, based on its own analytics software, 80% of clicks on its advertisements within Facebook had come from fake users.

The company tried to contact Facebook to discuss the issue because they discovered "bots were loading pages and are the reason for increasing advertising cost, however Facebook was not available for contact.

More and more advertisers have been challenging Facebook to prove that the clicks the have been receiving are real.

Facebook claims to now be looking into the concerns.