Experts often raise significant red flags about Telegram's security model, primarily because its robust protections are not the default settings.

While Telegram is generally a secure application compared to many standard messenger apps, its default operation is a major point of criticism from privacy and security experts.

Top Red Flags Uncovered by Security Experts

1. End-to-End Encryption is Not Default

This is the single most criticized feature.

    The Default: Standard and group chats use Client-Server Encryption (often called "Cloud Chats"). This means messages are encrypted as they travel from your device to Telegram's servers and from the servers to the recipient, but Telegram holds the decryption keys and stores the messages on its servers. Technically, Telegram or an attacker who compromises the servers could access these messages.

    The Secure Option: Only "Secret Chats" use End-to-End Encryption (E2EE), where only the sender and receiver can read the messages. The catch is that users must manually enable a Secret Chat for each contact, and they are not available for groups or public channels.

2. Proprietary Cryptography (MTProto Protocol)

Telegram developed its own encryption protocol called MTProto, which is generally frowned upon by the cryptography community.

    Custom-Built Crypto: Security experts prefer established, peer-reviewed, open-source protocols (like the Signal Protocol) that have been rigorously tested and broken by experts over years.

    Lack of Peer Review: Creating a new encryption protocol is complex and prone to subtle errors. Critics argue that MTProto has not had the same level of independent, public scrutiny as industry standards. Past security analyses have identified and required fixes for vulnerabilities in earlier versions of MTProto.

3. Closed Server-Side Code

While Telegram's client-side apps are open-source, the server-side code is proprietary and closed.

    Trust Requirement: This means outside security researchers cannot audit the entire architecture to verify that the encryption and data handling on Telegram's servers work as claimed. Users must simply trust Telegram with their data.

4. Metadata Collection and Storage

Telegram, like many services, stores a significant amount of metadata for all users, including those in Secret Chats.

    What is Stored: This metadata includes your IP address, username, phone number, and the precise time you were online (last seen).

    The Risk: Even if your message content is E2EE, this metadata can be valuable for surveillance and can be subject to government or law enforcement requests, which Telegram's policy may sometimes comply with under specific legal frameworks.

Summary: Is Telegram Secure?

Scenario   Security Assessment   What It Means
Standard/Group Chat   Low Security (Client-Server Encrypted)   Telegram can technically access your messages and data is stored on their cloud servers.
Secret Chat (E2EE)   High Security (End-to-End Encrypted)   Only the two participants can read the messages; they cannot be forwarded or accessed by Telegram.
Compared to Others   Average   Less secure by default than Signal (which is E2EE by default), but generally more secure than unencrypted apps like Facebook Messenger.

For maximum privacy, security experts consistently recommend using an application that enforces End-to-End Encryption by default for all conversations. If you use Telegram for sensitive communications, you must use the Secret Chat feature.