uest and response messages contain header fields that can conceal information which can be rendered by a UA. This kind of information can help SPITters to send large messages since the attributes of these header fields allow (dynamic length, extent to multiple lines) or to perform other C 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security TABLE 19.1 Response Messages and Their Possible SPIT Content Response messages Possible SPIT content Provisional (1xx) The message bodies might include session descriptions 180 Ringing The message body might contain textual information, or an audio file, or even animations 182 Queued It might contain a reason phrase, illustrating further details about the status of a call, or a message body that play an audio file, from an on-hold music palette. 183 (Session Progress) The Reason-Phrase or message body of it could provide additional details. 200 OK It might contain returned information that depends on the method used in the request 300 Multiple Choices It might include a message body 380 Alternative Service It might contain a message body in which the alternative services are described. 480 Temporarily Unavailable It might contain a reason phrase indicate a more precise cause, such as why the callee is unavailable 484 Address Incomplete It might contain a reason phrase 488 Not Acceptable Here It might contain a message body with a description of media capabilities 606 (Not Acceptable) It might contain a message body action as to trigger the UA to execute the body. The main header fields of SPITters' interest and the way they can be exploited are: Subject: Might be parsed by the user's software and displayed to the user's terminal. From: Allows a text to be displayed to the user. Alert-Info: Specifies an alternative ring back tone that could be used as a pre-recorded audio SPIT message. Call-Info: Some parameters of the specific header, i.e., purpose, icon, info and card, could be used for sending SPIT messages. Contact and To: The display name 