Enabling the Contact Sync feature in the official Facebook iPhone and iPod touch application actually uploads all of a user’s contact info from the device to Facebook, a report in The Guardian reveals. Once the sync option is enabled, all of the contacts stored on the iPhone or iPod touch are uploaded to Facebook along with their names, e-mail address and phone numbers. This information is stored in the user’s Facebook Phonebook and linked to each contact’s Facebook account based on their matching e-mail addresses or phone numbers.
Linked accounts are not limited to the user’s friends, however; non-friends are included and even users who have hidden their Facebook profiles from normal searches will appear linked in this view if they have listed a phone number or e-mail address on their profile. Contact information on non-Facebook users is also stored in the phonebook with the option to invite those friends to join Facebook.
Apple’s new App Store Guidelines published early last month expressly prohibit applications from transmitting “data about a user without obtaining the user’s prior permission and providing the user with access to information about how and where the data will be used,” a restriction that could be read to apply here.
Although the current version of the Facebook app does provide a warning when enabling the Contact Sync feature, this warning does not make it clear to the average user exactly how their contacts’ information will be used by Facebook beyond stating that the information will be “subject to Facebook’s Privacy Policy.” Further, other Facebook users who have privately listed their phone numbers or e-mail addresses may not be aware that this information may be used to locate their Facebook account, even when it is otherwise hidden from normal searches. iPhone users can opt-out of the Contact Sync feature by simply disabling contact sync in the Facebook app, then visiting their Facebook Phonebook page from a web browser and following the link on the right-hand side to remove mobile contacts from Facebook.