There are possible causes from the physiology that arises from poor sleep, but also the fact that when sleep-deprived it’s difficult to live a healthy life – there is more drinking, more obesity, less exercise, more smoking etc – and these may be what causes any possible increased risk.

They've already called out that it's just an association, more work is needed to show if there's actually causality

3:31 here!

At least from the folks I've talked to he is not well-liked

Signal is open source, right? Though that wouldn't stop a bugdoor, it might at least make one harder. As you say, I think getting in through the OS itself is much more likely. Signal would put up much more of an ideological fight than Google, I imagine.

I mean, unless somebody is burning browser zero days on random public QR codes I'm not too worried.

This was my first Discworld novel! Highly recommend.