Economic assessment of externalities for interactive audio media anti-SPIT protection of internet services

Spam over internet telephony (SPIT) refers to all unsolicited and massive scale attempts to establish voice communication with oblivious users of voice over internet protocol (VoIP) services. SPIT exhibits a significant increase over the last years, thus developing into a serious threat with adverse impact and costs for the business economy. An audio completely automated public Turing test to tell computers and human apart (CAPTCHA) has been introduced as a means to distinguish automated software agents (bots) from human. CAPTCHA has been proposed as a security measure against SPIT. In this paper, we lay the principles for an adequate understanding of the SPAM-related economic models, as well as their analogies to the SPIT phenomenon, so as to weigh the benefits of audio CAPTCHA protection against the incurred costs. Our approach is based on the economic assessment of externalities, i.e., the economic impact associated with the SPIT side effects on the everyday life.