I remember his answer on whether users are tracked when logged off. I mean the answer can really be a very simple Yes. But instead we got this evasion (I lightly cleaned up):
WICKER: One other thing: There have been reports that Facebook can track a user's Internet browsing activity, even after that user has logged off of the Facebook platform. Can you confirm whether or not this is true?
ZUCKERBERG: Senator — I — I want to make sure I get this accurate, so it would probably be better to have my team follow up afterwards.
WICKER: You don't know?
ZUCKERBERG: I know that the — people use cookies on the Internet, and that you can probably correlate activity between — between sessions.
We do that for a number of reasons, including security, and including measuring ads to make sure that the ad experiences are the most effective, which, of course, people can opt out of. But I want to make sure that I'm precise in my answer, so let me ...
WICKER: When — well, when you get ...
ZUCKERBERG: ... follow up with you on that.
[1] https://www.washingtonpost.com/news/the-switch/wp/2018/04/10...