Ask HN: How can an external app track WhatsApp online status/last seen?

2 points

4 years ago

I saw a WA tracker app today, that reminded me of time when I found WhatsDog[1]. You enter a number in the app and it tracks user's online status in the background. It used to work.

Back then (4-5 years ago), I remember de-compiling to understand the tech but couldn't find anything.

How does this work/used to work?

My guess is that they would be using the loophole where anyone can see if the user is online (even if the user hasn't saved your number[2]) and replicating requests like WhatsApp web client. Doesn't sound a good/scalable solution to me.

[1] https://whatsdog.en.uptodown.com/android There are many more (https://play.google.com/store/search?q=whatsapp%20tracker&c=apps&hl=en_IN&gl=US), some would be definitely fake.

[2] https://www.indiatoday.in/technology/news/story/whatsapp-has-status-flaw-stalkers-are-using-it-to-track-women-online-using-automated-apps-1791129-2021-04-15