Key points:
Most widely used messaging app
Uses the same encryption protocol as Signal
Collects heaps of your data
Free, but owned and operated by Meta
WhatsApp is the most popular private messaging app on this list, with about 2 billion monthly users, according to Exploding Topics. Because it's so popular, there's a higher chance that other people you might be chatting with have WhatsApp, and therefore your chats can be encrypted. And if the person you're chatting with doesn't have WhatsApp -- or any of the other messaging apps on this list -- then your messages might not be encrypted.
WhatsApp uses Signal's encryption protocol, so your chats and calls are just as end-to-end encrypted as those on Signal. But the main distinction between Signal and WhatsApp is that the latter collects loads more user data, even compared to Telegram.
According to WhatsApp, it automatically collects information like your usage and log information, device and connection information, location information and cookies from you when you use the app. And other people on the app can provide WhatsApp with information about you, too.
"When other users you know use our Services, they may provide your phone number, name, and other information (like information from their mobile address book) just as you may provide theirs," WhatsApp writes in its privacy policy.
That means even if you don't use the app much and only use it to chat with a friend or relative overseas every few months, your data can still end up in WhatsApp's hands via your friend or relative.
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