or in their annual revenue losses. Beside the financial impact, it might also constrain new service deployment and adversely affect the customers perception. Fraud activities can fit into two main categories. The non revenue fraud happens when a service is used with the intention of avoiding the costs but without the intention of making money. It includes providing no-cost services to friends or private usage. However, revenue fraud intends financial benefits as in call selling or premium rate services fraud. Fraud is a general menace being faced by many of fields including, credit cards, e-commerce, insurance and telecommunications. VoIP is an emerging technology and as with most existing Internet applications, it will certainly be the target of fraud and misuse in the future. As a consequence, in today's financial environment, fraud detection has become a necessity in order to maintain a successful business. To realize how fraud detection and prevention is important, it is worth mentioning that for the high data traffic of 400000 transactions per day, a reduction of 2.5% of fraud triggers a saving of $1 million per year. 24.2.3 Fraud in VoIP In traditional telecommunication networks, various experts estimate that fraud accounts for annual losses at an average of 3-5% of the operators' revenue and is still increasing at a rate of more than 10% yearly. Hence, with the openness of VoIP technology, one can expect an even higher threat of fraud and higher losses of revenue. Actually, there has already been various press reports about identity stealing and misuse of services in the Internet, which makes fraud the biggest threat to VoIP providers currently. © 2009 by Taylor & Francis Group, LLC SIP Handbook: Services, Technologies, and Security In traditional telecommunications, service fraud can take different shapes including: Call selling: sale of high tarif calls below their market value with the intent of evading payment to the operators. Surfing: use of another person's service by illegally obtaining his access 