An Instant Messaging security system that encrypts Instant Messages sent by a Instant Messaging user to an Instant Messaging server by intercepting the messages, negotiating a preferred security algorithm and forwarding the encrypted messages to the server. The security system intercepts and decrypts encrypted messages sent by the server to the user. The security system is able to determine whether a receiving user is equipped with a similar security system without prior knowledge of network addresses, configuration or capability. The security system is transparent to the Instant Message service provider and may provide one or more indicators to users that messages are encrypted during forwarding.