(CNN) -- Facebook CEO Mark Zuckerberg talks about "sharing" info and "connecting" people to each other more than Kanye West talks about himself. And the site's mission statement hits those themes hard, saying Facebook's goal is to give people "the power to share and make the world more open and connected."
So it might come as a surprise to Facebook users that the site takes a do-as-I-say-not-as-I-do approach to letting people share their own information with one of its biggest competitors.
In what's been called "data hoarding," Facebook will not let users export their Facebook contacts lists -- which include pictures and e-mails -- to Google's e-mail system.
That's not new, but Facebook's anti-sharing policy has come under scrutiny recently since Google last week retaliated by blocking users from uploading their Gmail contacts to Facebook, according to TechCrunch.
"We're disappointed that Facebook didn't invest their time in making it possible for their users to get their contacts out of Facebook," a Google spokesperson wrote in an e-mail to CNN. "As passionate believers that people should be able to control the data they create, we will continue to allow our users to export their Google contacts."
Facebook did not respond to a CNN request for comment.
At first read, this may sound kind of silly or irrelevant -- two multibillion-dollar tech companies bickering with each other. But these companies hold the keys to millions of peoples' online identities. They control whether you can download or export lists of your contacts, where on the internet you can use those lists, and which data companies they'll sell this information to.
The new lockdowns on user data could signal a change in how the Web works, writes Michael Arrington from TechCrunch.
The big tech companies are now in a "data war," and it may be hard to stop this escalation now that it has started, writes Arrington, who sees Facebook as the aggressor in this situation.
Facebook "just pretty much refused to let users export social graph data, even though they import it like crazy from every source they can get their hands on," he says.
The Wall Street Journal compared the situation to "what happens when a 6-year-old and a 12-year-old get in a fight." (Facebook is the 6-year-old, apparently.)
"Expect neither side to let go easily," Geoffrey A. Fowler writes.
Despite this fight, it's still possible to share your contacts among plenty of websites, which makes it easier to find friends on social networks and to synchronize the digital contacts you've accumulated from various sources.
Below is a list of four of the big players in the online contacts space, and who shares with whom, compiled from each of these sites' contacts pages. This should give you an idea of how "trapped" your data is in any one of these services. (Note that companies who are "friends" -- i.e. Facebook and Microsoft, since that company owns a stake in Facebook -- tend to be fans of sharing data. Rivals like Google and Facebook -- not so much):
Who holds onto your data?
Google: Exports contacts to Facebook, Microsoft and Yahoo
Facebook: Exports contacts to Microsoft, Yahoo (not Google)
Microsoft: Exports contacts to Google, Facebook and Yahoo
Yahoo: Exports contacts to Google and Facebook (not Microsoft)