It will sometimes even block efforts of users to copy or migrate that data to other services or back it up onto their own storage media, almost as if it views your personal data as its corporate property.
Oh, Facebook also installs persistent cookies that remain active in your system for up to a month after you log in to the service that will automatically log you (or whoever is using your computer) in to Facebook automatically when you visit, or when you click a Like button on other sites – thereby tracking your activity outside the Facebook network.
It may be prosecuted under U.S. federal wiretapping laws for that one. No federal charges have been filed, though there are plenty of lawsuits being filed by customers annoyed at being spied on and specifically angry that Facebook twice denied doing it and twice claimed to have stopped.
That should be the big privacy concern about Facebook according to security and privacy experts who compare the breadth of information it collects and refusal to admit to the secret police of some authoritarian countries.
That may be a little extreme in that we don't know of anyone Facebook has actually executed.
It's still a lot of private information and a lot of power for an online service to hold over millions of consumers who might prefer their private conversations not be made public or sold to commercial interests that, like Facebook, clearly don't have the customer's best interests in mind.
When security is a problem, add ways to avoid passwords!
So, on how many levels is it disturbing that as a "security" measure, Facebook has created the social-network version of the neighbor to whom you give a house key in case you're ever caught away from home and have to call to ask if they'll go over to water the plants, the dog or the children?