Facebook estimates that there are now more than 83 million 'fake' users on the social network, according to data released this week.

The social network said 8.7% of its 955 million active users might not be real.

There may be individuals who maintain one or more Facebook accounts in violation of Facebook's terms of service. The company estimates that "duplicate" accounts (an account that a user maintains in addition to his or her principal account) may have represented approximately 4.8% of its worldwide user base as of June 30, 2012.

Facebook also seeks to identify "false" accounts, which the company devides into two categories: (1) user-misclassified accounts, where users have created personal profiles for a business, organization, or non-human entity such as a pet (such entities are permitted on Facebook using a Page rather than a personal profile under Gacebook's terms of service); and (2) undesirable accounts, which represent user profiles that Facebook determines are intended to be used for purposes that violate its terms of service, such as spamming. As of June 30, 2012, Facebook estimates user-misclassified accounts may have represented approximately 2.4% of its worldwide users and undesirable accounts may have represented approximately 1.5%.

Facebook's business model relies on targeted advertising and the company is coming under scrutiny over the worth of its advertising model which promotes the gathering of "likes" from users.

A number of advertisers have been challenging Facebook to prove that the clicks they are receiving on their ads are "real" - these figures will provide them with added ammunition.

"We generate a substantial majority of our revenue from advertising," the company said in a filing to US SECURITIES AND EXCHANGE COMMISSION.

"The loss of advertisers, or reduction in spending by advertisers with Facebook, could seriously harm our business." 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.

"Bots were loading pages and driving up our advertising costs. So we tried contacting Facebook about this. Unfortunately, they wouldn't reply.

"Do we know who the bots belong too [sic]? No. Are we accusing Facebook of using bots to drive up advertising revenue. No. Is it strange? Yes," Facebook said in a post on its page.