Earlier quoted context omitted.
When you are online anyone can check it. There is no option to hide the online status. Using an easy script anyone can then spy and understand pretty much everything of a person, or a group. This is easy cyber stalking and dangerous. Especially because normal people do not understand this and think that hiding last seen is useful to avoid being stalked…
You can absolutely hide it - it's in the settings, as mentioned in the article. The tradeoff is you won't be able to see anyone else's status. I do agree I don't particularly like that it's on by default.
> Please note you can't hide your online.
https://faq.whatsapp.com/general/chats/about-last-seen-and-o...