Facebook, Twitter and Google face questions from US senators

The chief executives of Facebook, Twitter, and Google are being quizzed by the US Senate over a key legal protection given to their firms.At present, the firms cannot be sued over what their users post online, or the decisions they make over what to leave up and take down.But some politicians have raised concerns that this "sweeping immunity" encourages bad behaviour.The three CEOs say they need the law to be able to moderate content.As the hearing began, Facebook's Mark Zuckerberg vanished, unable to connect to the committee meeting - something that Republican Senator Roger Wicker labelled a "most interesting development".But after a brief recess, Mr Zuckerberg told politicians that he supports changes to the rule "to make sure it's working".Mr Zuckerberg, Twitter's Jack Dorsey and Google's Sundar Pichai were summoned before the Senate after both Democrats and Republicans backed a subpoena vote.IMAGE COPYRIGHTEPAimage captionMark Zuckerberg was 'unable to connect' to the committee initiallySenators are worried about both censorship and the spread of misinformation.And some industry watchers agree that the legislation - known as Section 230 - needs to be revisited."[It] allows digital businesses to let users post things but then not be responsible for the consequences, even when they're amplifying or dampening that speech," Prof Fiona Scott Morton, of Yale University, explained to BBC's Tech Tent podcast."That's very much a publishing kind of function, and newspapers have very different responsibilities. So we have a bit of a loophole that I think is not working well for our society."