Hackers could have full access (!) to everything on the phones of WhatsApp users.
This was possible through a security issue disclosed by WhatsApp itself last week. All a hacker had to do to control your phone was send you a malicious video or start a video call with you on WhatsApp.
You are probably thinking "Yeah, but if I updated WhatsApp to the latest version, I am safe, right"?
A WhatsApp security issue exactly like this one was discovered in 2018, then another in 2019 and yet another one in 2020 (tap each year's link to see the corresponding vulnerability). And yes, in 2017 before that. Prior to 2016, WhatsApp didn't have encryption at all.
Every year, we learn about some issue in WhatsApp that puts everything on their users' devices at risk. Which means it's almost certain that a new security flaw already exists there. Such issues are hardly incidental – they are planted backdoors. If one backdoor is discovered and has to be removed, another one is added (read the post "Why WhatsApp will never be secure" to understand why).
It doesn't matter if you are the richest person on earth – if you have WhatsApp installed on your phone, all your data from every app on your device is accessible, as Jeff Bezos found out in 2020. That's why I deleted WhatsApp from my devices years ago. Having it installed creates a door to get into your phone.
I'm not pushing people to switch to Telegram here. With 700M+ active users and 2M+ daily signups, Telegram doesn't need additional promotion. You can use any messaging app you like, but do stay away from WhatsApp – it has now been a surveillance tool for 13 years.