Facebook has rushed to respond to panicked users after it was revealed the social networking site was storing numbers belonging to those stored in the mobile device used to access the website's mobile app.
The Phonebook Contacts feature has been live for "a few years", though many users are just noting its existence, reported the Huffington Post.
The Contacts list may include numbers from users' cell phones that did not link to Facebook accounts.
Facebook was quick to respond to rumours that phone contacts were visible to everyone.
"Rumors claiming that your phone contacts are visible to everyone on Facebook are false" said Facebook.
"Contacts list, formerly called Phonebook, has existed for a long time. The phone numbers listed there were either added by your friends themselves and made visible to you, or you have previously synced your phone contacts with Facebook."
However, PCWorld's Dan Tynan claims that he is not even friends with some of the users in his Contacts list.
"There are also people whom I do not know, who are not in my Android phone's contact list, with whom I share no connection whatsoever and have no friends in common, who are in my Facebook phone book."
The personal Phonebook is accessible from a Facebook profile under the "Edit Friends" option on then account tab, then by selecting "Contacts" on the sidebar menu.
To remove a phone number from Facebook, click "Edit Profile" to change contact information.