) are as follows: - Imitation of attack: unauthorized users can try to access IN services. For example, in the case of IMR service a user not recorded can try to view video services. - Simulating attack: an authorized user can try to avoid security policy and illegitimately obtain access to sensitive services. For example, a user with common access privileges can try to act as an administrator of service IN. - Denial of Service attack: an adversary can try to block users to access service IN. For example, by sending a great number of requests to the system simultaneously. - Communication to spy and alter: an adversary can try to spy and/or to modify the communication between a legitimate user and elements of service IN. - Lack of responsibility: if IN is not capable of verifing the communication between users and its elements of service, then it will not be possible to make users responsible for their actions. This list is not exhaustive, in practice one can be confronted with other prob- lems of security, not belonging to the area of application (for example, prob- lems linked to the policy of security, to the security of management systems, to the placement in action of the security, to the security of the implementation, to the operational security or to the processing of security incidents). As the technological evolution of software increases in a manner not estimable, simi- larily the technological connection tools to the system and the attack passive C 2009 by Taylor & Francis Group, LLC Secure Intelligent SIP Services and active also become inestimable. If the system and its components are not sufficiently secured, many threats can occur. However, it is necessary always to consider: What is the probability of a threat (occurrence; likelihood)? What are the potential damages (impact)? What are the costs to prevent a threat? Depending on these suppositions, the cost and the efficiency of security mech- anisms should be implemented. The potential of the threat depends on the implementation of IN and the spec