Dive summary:

• In its earnings release last week, Facebook estimated that 8.7% of the 955 million accounts on Facebook are false or fake.
• 4.8% are duplicate accounts, 2.4% are user-misclassified accounts, and 1.5% are undesirable accounts
• The number is a big jump from March, when the company estimated that 5-6% of its accounts were false or duplicate.  The jump in the total number is due to additional classifications on accounts it considers "false".

From the article:

Last week, during its first quarterly earnings report as a public company, Facebook revealed it had 955 million monthly active users and 543 million monthly active mobile users. In the social-networking giant's 10-Q filing published last night, the company disclosed that nearly 20 percent of the latter number, 102 million users, accessed the social network in June solely from their mobile device.