Stateless human detection for real-time systems allows a real-time message system to challenge incoming messages suspected of being generated by an automated application. When a suspect message is detected, a challenge is presented to a sender of the message. The challenge is designed to require human intervention to provide a correct answer to the challenge. A challenge packet is sent with the challenge and includes a challenge answer and, possibly, a server identifier, a challenge identifier and/or a time stamp that can be used to prevent attacks on the challenge. The challenge packet is encrypted so that the sender cannot access the contents thereof. When the sender provides a response to the challenge, the sender returns the challenge packet. The challenge packet is decrypted and the challenge answer is compared to a sender answer. If the answers match, the sender is allowed subsequent access to the messaging system.