Facebook iPhone Contact Sync Feature is Latest Fear Target

UPDATED: Facebook’s Sync Contacts feature on its iPhone (s aapl) app is the latest target of fearful critics who are wondering if the social networking giant has gone too far in peering into your personal information.

The concern is raised by the Guardian’s tech blogger Charles Arthur, who points out that the syncing feature on the iPhone app does more than just push out your friends’ profile pictures and info to your phone’s contact list, which is what most people assume. Syncing makes it such that, “all contacts from your device (name, email address, phone number) will be sent to Facebook and be subject to Facebook’s Privacy Policy and your friends’ profile photos and other info from Facebook will be added to your iPhone address book,” according to a warning notice prior to syncing.

Arthur’s concern, which is built largely off a previous blog post from developer Kurt von Moos, is that Facebook now has access to all your contact data from your phone, and he worries that Facebook can take that information from your phone list and share it on Facebook. Or if someone obtains your phone, they can access all your friends’ information. Another blogger worries that sharing of data without user consent actually violates Apple’s App Store guidelines.

Arthur points to your Facebook phone list as a way to suggest that there are phone numbers inadvertently shared by your friends after syncing their phones. I’m not quite certain about that, because most of the numbers in my list appear to have been pulled from the profile page information that my friends willingly gave up.

The basic worry from Arthur is that Facebook hasn’t been upfront about pulling your data from your phone and explaining what it’s doing with that information. Even with the notice from Facebook prior to syncing that you should “make sure your friends are comfortable with any use you make of their information,” he warns that Facebook is in possession of more of your data than you might have realized.

Facebook is no stranger to privacy concerns. The company routinely pushes the boundaries, then retreats occasionally in the face of opposition. This issue touches on some of the inherent security concerns around cloud services, which, by their nature, store some of your personal data on remote servers. But this isn’t exactly new. Google (s goog) and Apple have lots of your personal information and contact data stored in the cloud. Palm (s hpq) also brought similar features with its Synergy interface.

While there’s a legitimate concern about how Facebook handles this cell phone data — something I hope they further clarify — it also speaks to just how big a target Facebook has become. The company has grown in size to the point that, like Google, it can’t do much without prompting warnings from critics. With more than 500 million users, Facebook enjoys an ubiquity that can be unnerving for many. It behooves Facebook to be even more cautious with future moves or at least, provide even more transparency, especially for less savvy users who are increasingly entrusting more and more of their lives to the social network.

UPDATE: Facebook refuted Arthur’s charge Thursday and said synced phone numbers from a mobile phone are not shared with a user’s friends online but are only available in a user’s private phone list. That would make them vulnerable to hacking but it’s no different than any other cloud service, a spokesperson told the Main Online.

“Only you can see your Phonebook on Facebook; it can’t be seen by anyone else,” the spokesoman said. “This is the same as online phonebooks or email contact lists many people already have.”

Related research from GigaOM Pro (subscription req’d):

Post and thumbnail photos courtesy of Flickr user mollybennett