According to the Sina Technology News, Facebook admitted that a security bug had accidentally exposed 6 million users' contact information (emails or phone numbers).

After Facebook announced the discovered bug on Friday, it claimed its team would fix it in 24 hours. 

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Facebook has also post a statement in its blog to explain and address the issue:

"We recently received a report to our White Hat program regarding a bug that may have allowed some of a person's contact information (email or phone number) to be accessed by people who either had some contact information about that person or some connection to them.

Because of the bug, some of the information used to make friend recommendations and reduce the number of invitations we send was inadvertently stored in association with people's contact information as part of their account on Facebook. As a result, if a person went to download an archive of their Facebook account through our Download Your Information (DYI) tool, they may have been provided with additional email addresses or telephone numbers for their contacts or people with whom they have some connection. This contact information was provided by other people on Facebook and was not necessarily accurate, but was inadvertently included with the contacts of the person using the DYI tool."

In addition, as well as fixing the problem on its security and privacy, Facebook has also updated its iOS app with new privacy features.