e-mail spam was sent to 600 addresses. In the late 1970s and early 1980s there was not any real public Internet, and thus the growth of e-mail spam was not as exponential as it is today. Today, there is widespread use of the Internet and, since 2004, there has been significant growth in mass-market VoIP services over broadband Internet access services, in which subscribers make and receive calls as they would over the Plain Old Telephone Service (POTS) or Public Switched Telephone Network (PSTN). Thus, due to the current status of the Internet and the pen- etration of VoIP services, including the foreseeable IP Multimedia Subsystem (IMS) paradigm shift, it is likely we will see SPIT spread rapidly around the world. In fact, it is accepted to happen more sharply in the VoIP world than the e-mail world, since "vishing" attacks, i.e., acquiring sensitive information, such as usernames, passwords and credit card details by masquerading as trustworthy entity using VoIP services, are expected to increase by 50% during 2008, according to industry reports [1]. The explosion in the adoption and usage of VoIP together with the knowl- edge gained SO far by spammers in the e-mail spam domain, and of course their potential profits of spam business, makes it more challenging to design and deploy an anti-SPIT framework. Additionally, VoIP services, and espe- cially Session Initiation Protocol (SIP) when used as the signaling bearer for VoIP session management, significantly differ from classic SMTP e-mail services. Therefore, some of the existing and reliable mechanisms for preven- tion, detection and management of spam might not be applicable. Finally, even if we assume that spam and SPIT threats are equivalent, the SIP proto- col itself might illustrate some new, probably more fatal, vulnerabilities and weak points. In this case, SPITters might find themselves luckier than their predecessor spammers. If SPIT prevalence becomes proportional to spam, then the acceptance of VoIP will be encumbered. This might be a problem from t