The industry momentum for data portability brotherhood hit a bump on Thursday when Facebook blocked Google's Friend Connect service from accessing Facebook members' data.

Friend Connect violates Facebook's terms of service because it "redistributes user information from Facebook to other developers without users' knowledge," Facebook official Charlie Cheever wrote on the company's blog for developers.

"Just as we've been forced to do for other applications that redistribute data in a way users might not expect or understand, we've had to suspend Friend Connect's access to Facebook user information until it comes into compliance," Cheever wrote.

For its part, Google doesn't fully understand what it needs to do in order to comply with Facebook's terms of service, said Google Engineering Director David Glazer in a phone interview.

"We think users should be in control of their data. When we built Friend Connect, we designed it very carefully to put users in control of their information at every step of the way. We're disappointed that Facebook chose to disable their users' ability to use Friend Connect with their Facebook friends," Glazer said.

Google shares Facebook's beliefs that users need to be in control of their data and that their privacy needs to be respected. "I agree strongly with the values they assert, and I believe the APIs they have released do a good job of honoring those values. I don't understand at this point why they've chosen to do something that doesn't align with those values," Glazer said.

Google held talks with Facebook before and after the announcement of Friend Connect on Monday around the issue in question, and conversations are ongoing, Glazer said.

Although Friend Connect is in a limited preview, there are four Web sites -- two built as demos and two real ones -- that had been accepting requests from users to grab their Facebook profile data, Glazer said. That functionality is now interrupted, he said.

Facebook didn't respond to a request for comment beyond Cheever's blog posting.

Friend Connect, Facebook Connect and MySpace Data Availability are separate initiatives announced in the past week designed to let people reuse the content from their social network profiles in other sites.

The main idea behind this data portability concept is to save people from having to reenter into multiple sites common profile information like their personal interests, list of friends, photos, video clips, blog postings and the like.

However, none of the three initiatives even comes close to providing a broad data portability solution, although MySpace, Google and Facebook have been commended by industry observers for at least taking some first steps to address the issue.

It's not a secret that data portability itself is a complicated matter to solve due to significant technical as well as commercial and operational challenges that surround it.

Thursday's move by Facebook highlights just one of the considerable obstacles for data portability: the different user-privacy policies and settings that exist among social networks and online service providers. These policies and settings need to be reconciled and harmonized in order for them to share and accept user data from each other.

Google didn't immediately respond to a request for comment about Facebook's decision to block Friend Connect.