Why is this a "security" issue? People know that other people can see their "last seen" date, but usually they don't care so they left it. Hell, I leave it public as well. I couldn't care less about this tiny details.

Now, if you tell me that by leaving public my "last seen" date, people can get more data about me (e.g., with whom I talk to), well then yes, I would call that a security issue.

> if [...] people can get more data about me (e.g., with whom I talk to) [...]

It's quite possible, at least among mutual friends. If you have 2 people you know, who are also friends with each other, who have high correlation of online times, then, it's a signal that they could be talking with each other.

It's also amusing (insert a better verb...) that Facebook probably knows who's dating who based on frequency of messages on Messenger/WhatsApp/Instagram, location data ("It's the 3rd Friday night that their phones are close to each other in some venue"), and if they're on the same WiFi (A few hours later: "Well, it's 1AM, and after an hour of inactivity, James' phone is now connected to Jenny's WiFi, they did have their third date earlier...")

Reminds me of this talk: Spiegel Mining at the C3 https://www.youtube.com/watch?v=-YpwsdRKt8Q

What was interesting in my writing is that a simple API request quota could be preventing me from scraping this much.

Not sure why you are webscraping, there is a Whatsapp business API you can use to gather a lot more information.

Here is a github repo that implements it, including generating text QR code.

https://github.com/Rhymen/go-whatsapp

The most interesting part to me wasn't the technical details but rather the MAU, WAU, DAU stats at the end from random sample. Way fewer people than I would have expected use WhatsApp on a weekly basis.

This is in France, where text messages were free (unlimited with your subscription) long ago before we had internet on our smartphone. Thus people use text message a lot and did use WhatsApp only to contact people outside from France

Text messages were around €0.10 for most plans until 2012 though (due to the unlawful collusion of telcos).

Not in France actually, we mainly use WhatsApp as a main message app; nobody uses SMS nowadays

Well I do use SMS, as well as my friends and family in France.

I use WhatsApp with Belgians (I live in Belgium) because SMS's are not free for them, and also for sharing photos because MMS is a mess.

true, my point is more about the tendency of using groups of people to quickly share. Which SMS does not do properly.