The Alertus Desktop client will only contact the server it is configured to look for.  Once a connection is made, cryptographic verification is used.  Specifically, each organization is issued a uniquely identifiable encryption key, and a matching certificate which is securely signed by Alertus.  The client requests this certificate from the server, and verifies that it was issued by Alertus.  When the server sends a message, it uses the encryption key to digitally sign the message.  If the signature is invalid, or the certificate was not issued by Alertus, the message will not be displayed.