Instant Messaging. Also known as chatting, texting, or DMs.
We love to text each other. It's become the default mode of communication for nearly everyone. It's asynchronous, it's quick, it's lightweight, it's searchable, it's reliable, it's flexible. It allows for freedom in communication that no other form of communication has achieved.
So naturally, I am here to ruin this for you as well.
Data Retention
So one of the pros of IMs that I mentioned is that it's searchable. If someone sends me a message - their address, details for some event, anything - that I need to look at again, I can tap the little magnifying glass icon and search for that message. The message isn't deleted (unless by sender's choice, receiver's choice, or Snapchat) so it is convenient for me to look it up.
But where are all the messages stored to enable this lookup? Is it on your phone, or on a server somewhere?
If it's on a server somewhere, is it protected against hackers? Is it protected against employee voyeurism? Is it protected against government warrants? Is it protected against targeted ads? Is it protected against LLM training?
And if you delete your messages or account, are those messages deleted from the servers as well?
So What Apps Should I Use?
Unfortunately, this isn't a decision that's completely yours. You can switch to a private email service, a private operating system, but to switch to a private IM app, you need all your friends to be on it.
What I do is to have a set of apps, and try to keep as many conversations on the more private apps as I can.
Signal
The best option currently available, in my opinion. Open-source, zero-trust app. It assumes the server is being spied upon, and its encryption systems act as such. Open-source means that its encryption is verifiable. Even the server code is open source. They even use post-quantum cryptography, if I'm reading their blog correctly.
I nearly called this the gold standard, but I remembered I do have some complaints with it. You cannot easily host a signal server on your own. Their server code is open-source only for verification, even though there is no way to verify that the servers are running the same code. The apps are built to maintain security despite compromised servers - and if you do manage manage to host one, you cannot easily configure the client to use the new server.
Telegram
Positions itself on privacy. They claim to store every user's data on servers in at least two different countries, requiring multiple jursidictions to coordinate in order to reveal information about a user. They also tend to have good features before others IM platforms do. And their client-side code is open-source, so you can verify that Secret Chats are indeed secret, with end-to-end-encryption.
The negatives? They do end up complying with law enforcement requests to reveal information. Also, their default chats aren't protected with end-to-end-encryption, and Secret Chats are not synced like in Signal.
WhatsApp
Owned by Meta. Claim to have end-to-end-encryption, but clients are never open-source, so there's no trust. Also, it's Meta, so there's no trust. Still, one of the most popular IM apps so, tends to be used by nearly everyone.
Snapchat
Chats are not stored longer than 24 hours. Which infuriated me, as someone who hates to lose chats. No one with access to your phone can read your old chats, but again there's no trust about what Snapchat itself does with your messages.
Also, I hate the quantification of friendship in Snapchat.
Discord, Instagram, and other DM platforms
Data is often stored on the cloud, with no end-to-end encryption. There's no thought of privacy or security here, but they sure as hell are convenient!