The company has already faced questions over the legitimacy of clicks on the advertisements it sells. In July, a company called Limited Run, which has a platform used for selling digital music and merchandise, said it believed of the clicks it paid Facebook for resulted in users landing on its website.

Limited Run, based in Manorville, New York, declined requests for interviews after its accusation. It but maintains a presence on Tumblr and Twitter.

Shuman Ghosemajumder, a former Google employee who headed the company's efforts to fight click fraud, said in a recent interview that Facebook would have much more insight into questionable clicks than could be seen from the outside by an advertiser such as Limited Run.

For instance, Facebook can see how long a user's account has been open and monitor activity for suspicious behavior, such as if the user is liking hundreds of pages, where the clicks originate from and if the user has an irregular profile, such as having no friends.

People may think it's to the benefit of companies such as Google and Facebook to allow a bit of click fraud, but the true economics are that "if you provide best ROI [return on investment], all advertisers have an incentive to move their ads with you," said Ghosemajumder, who is now working with , a start-up specializing in security for social networking sites.