Everyone using the popular messaging app knows the fact that WhatsApp shows your "last seen" status by default. And some also know that the "last seen" data can be hidden through WhatsApp's settings.
But you can't hide the "online now" status which appears whenever you open the app. And that particular information is available to all WhatsApp users, not just to your contacts. So, anyone who knows your phone number, gets the information when you're online.
Now, there are tons of apps and services available that hook into that data. Basically, you download one of those apps and tell which phone number you want to start monitoring. Then, the app tracks, anonymously, when the given phone number appears online and records that. And as the app "pings" the status every 30 seconds or so, you'll soon get a full picture of when the particular user was using his/her WhatsApp.
From that data, after, say two weeks' worth of monitoring, one can easily draw conclusions on user's sleeping patterns, when they might have been in night club, etc.
And to make matters worse, two phone numbers' activity data can be bundled. Say, you suspect your spouse is chatting with someone who you don't exactly approve. By monitoring both, your spouse's phone number's activity and the suspected third party's phone number's activity, you can easily see íf they tend to be online at the same time (thus, implicating that they're chatting with each other).
There's currently no way to block such snooping, as WhatsApp wont allow users to block their online status at all. Only way that can done in order to counter the problem is to spoof the spy with "too much data", i.e. to keep WhatsApp open all the time, so that patterns can't be built. WhatsApp's official web client is handy tool to stay seemingly online all the time.
Written by: Petteri Pyyny @ 21 Sep 2020 5:54