Blumenthal and Markey also implied that Zuckerberg wasn't totally accurate when he told Congress that users had "complete control" over how they shared info and how people saw it. The politicians didn't confine their inquiry to device sharing, either -- they wanted to know what other data sharing methods Facebook had.

The senators asked Zuckerberg to provide answers by June 18th.

We've asked Facebook about the letter. However, the social network has already asserted that the sharing only existed so that it could provide Facebook on devices that (early on) didn't have apps. It maintained that it had tight control over data, and that user info was only ever accessible when people consented to sharing it. Not that this is likely to satisfy Blumenthal and Markey -- there's no guarantee they'll take action, but they clearly want more explicit promises of privacy than Facebook has offered so far.