Among the most popular encrypted messaging apps, Signal is widely considered the most secure and private option. While Telegram and WhatsApp offer encryption, there are significant differences in how they implement it and what data they collect.

Here's a breakdown of the three apps based on security and privacy:

1. Signal (The Clear Winner)
Signal is the gold standard for secure messaging and is often recommended by security experts and journalists. Its focus is on providing a private communication tool with minimal data collection.

Encryption: All communication on Signal is end-to-end encrypted by default, including one-on-one chats, group messages, voice calls, and video calls. Signal uses the open-source Signal Protocol, which has been peer-reviewed and is considered cryptographically sound.

Privacy: Signal collects the least amount of user data. It only requires your phone number to create an account. The app is funded by the non-profit Signal Foundation, so it has no financial incentive to collect and sell user data.

Transparency: The app's client-side code and server-side code are open source, allowing independent security researchers to audit it for vulnerabilities.

2. WhatsApp (A Strong Contender with a Major Caveat)
WhatsApp is the most widely used messaging app in the world, and it offers strong encryption for its users.

Encryption: All chats, calls, and media sent on WhatsApp are end-to-end encrypted by default, using a version of the same Signal Protocol. This means that neither WhatsApp nor its parent company, Meta, can read your private messages.

The Caveat: The major security concern with WhatsApp is its ownership by Meta. While the content of your messages is encrypted, Meta collects a significant amount of user metadata. This includes information like who you communicate with, when you communicate, and your location. This data is used for advertising purposes, which is a major privacy concern for many users.

3. Telegram (The Least Secure for Private Communication)
Telegram is popular for its large groups, channels, and cloud-based features, but it is the least secure of the three for private, end-to-end encrypted conversations.

Encryption: Telegram's encryption is not enabled by default. Only its "Secret Chats" offer end-to-end encryption, and this feature must be enabled manually for each conversation. Standard chats and groups are stored on Telegram's servers and are only encrypted in transit. This means that Telegram can technically access and read your messages.

Privacy: Telegram's privacy policy states that it may disclose users' IP addresses and phone numbers to authorities if they receive a court order confirming the user is a terror suspect. It also logs metadata and links accounts to phone numbers.

Security Concerns: The app uses its own custom encryption protocol, MTProto, which has been criticized by some cryptography experts for not being as transparent or rigorously tested as the Signal Protocol.