Zuckerberg hearing: Facebook founder attacked by US politicians for site's 'bias' and failure to protect users - as it happened

Richard Hudson asks about members of the armed forces who use Facebook – some of whom are in his constituency. Could that mean there's national security concerns by letting people have access to the kind of information that Facebook collects?

"I'm not specifically aware of that threat. But in general there are a number of national security and election integrity type issues that we focus on. The more input that we can get from the intelligence community as well encouraging us to look into specific things the more we can do that work."

Diamond and Silk again. "I have to bring [them] up again because they're from my district," says Hudson. But he doesn't actually seem to have a question about them – just wanted to mention them.

Oh OK: the Diamond and Silk question. What's the standard for offensive content? (Which is what got the pair deleted on Facebook.)

The first is threats of physical harm. But there's a broader standard of hate speech, which might make people feel unsafe in the community. What that is is something that Zuckerberg struggles with continuously, and he says they're criticised for their definitions from both the left and right.

Facebook talks about "bad actors" that led it to change its privacy policy in 2014. Who were they?

Zuckerberg doesn't remember. But Facebook saw a lot of people asking for information they didn't actually need, so it looked and that and said "hey, this isn't right". We should review these apps and make sure that developers need access to this data. Over time, Facebook made a series of changes that culminated in the one in 2014 that stopped developers getting access to people's friends.

Getting into a bit of partisanship here. (Not for the first time.) Democrats have been mean to Zuckerberg today but they were "high-fiving" when Obama won.

Zuckerberg being asked about the finer details of how people decide what they're sharing. Do Facebook users really know what they're doing?

He says it's quite clear. It shows the information it will be taking and why. And until you do it, nothing will happen.

The same with sharing content like photos. Every time, you can choose who to share it with.

So he says it's "quite clear".

Debbie Dingell is coming on the offensive – pointing out what Zuckerberg didn't know.

He didn't know about key court cases. He didn't know he couldn't be fined by the FCC. He didn't know what a shadow profile was. He didn't know what apps to audit. He doesn't even know all the kinds of information Facebook is collecting from its own users.

"Here's what I do know. You have trackers all over the web. On practically every website you go to, we all the Facebook like and Facebook share buttons. And with the Facebook pixel, people browsing the internet might not even see that Facebook logo. It doesn't matter whether you have a Facebook account. Through those tools, Facebook can collect information about all of us.

"So I wanted to ask you, how many Facebook like buttons are there?"

Zuckerberg doesn't know. Is it more than 100 million? It's been served more than that but he doesn't know the number of sites. He'll follow up on it. How many chunks of Facebook pixel code are there on non-Facebook web pages? He says she's asking for specific data, and he doesn't know about it – he'll get in touch after.

Dingell asks whether the Kogan data was sold to other apps than Cambridge Analytica. It took three years to find this out, she says – and she's worried we'll find other people in the same sort of time.

Zuckerberg says it's looking into all apps that had access to a lot of data. They'll make public any other apps they find that have been abusing data – and he suggests it's probably going to happen.

Is Facebook a publisher?

"There is content that we fund. Specifically in video today. When we're commissioning video to be created, I certainly think we have responsibility in that content. But the vast majority of content on Facebook is not something we commissioned. For that our responsibility is to make sure the content is not harmful" and is helping people build good relationships.

Buddy Carter from Georgia congratules Zuckerberg on the fact that he comes towards the end – so there's not long left now.