Instant messaging (IM) has become one of the most popular online communication tools among consumer and enterprise IM users. It provides instant message delivery, as well as convenient file transfer services. The increasing popularity and functionalities of IM programs have made it increasingly attractive for attackers, especially for worm writers. IM contact list offers worm an easy way of finding potential victims so that the worm could achieve a surprising spreading speed. This paper first presents our experimental results of simulating IM worm propagation in the logical network defined by IM contact lists, which is reported to be a scale-free network. Then, the existing proposals for detecting and containing IM worm epidemics are discussed. At last, a new algorithm for this purpose is presented, which is based on the observation of the bi-directional nature of IM worm traffic, and its advantages and possible improvements in implementation are analyzed. The simulation results show the proposed algorithm is of significant effect on restricting IM worm propagation. Instant messaging has grown at a phenomenal rate in the last several years to become a major form of communication both over the Internet and within company intranets. As one of the most successful and widely-deployed applications on the Internet, IM has increasingly become the target for attackers to propagate IM-borne viruses, worms, spam over IM (SPIM), malware and phishing attacks. Though widespread in adoption, IM is generally unprotected and unmonitored in consumer and enterprises environment, leaving it vulnerable to attacks and exploits. In 2005, real-time security threats associated with instant messaging, peer-to-peer and other real-time communication technologies increased 1 693% over 2004, with a total of over 2 400 unique threats. IM worms are the most prevalent form of IM malware, representing 90% of all unique attacks in 2005 [1] . These attacks frequently utilized social engineering techniques to lure end users into clicking on suspicious links embedded inside IM messages, enabling the activation of malicious code that compromised the security of host operating systems or applications. In addition, because each user generally has a list of "buddies", it is easy for the worm or virus to find new users and machines to infect. This means that IM worms have the potential to spread very quickly [2] .IM worms are worms that spread in IM networks,by
A hypersonic vehicle uses the airbreathing scramjet engine and the airframe and engine integrated design. Therefore, there is a strong cross-coupling effect among its aerodynamic force, thrust, structure, and control. The nonlinearity and uncertainty of the model cause difficulties in control system design. Considering the nonlinearity, coupling characteristics, and aerodynamic parametric uncertainty of its longitudinal dynamic model, we design the control law for its altitude system and velocity system based on the adaptive backstepping control method. Because of the feedback linearization method, we introduce the constraints of the flight vehicle’s actuator into the design, obtaining the robust adaptive control system constrained by the actuator of the flight vehicle. To avoid the high-order derivation problem of the feedback linearization method and the derivation of the virtual control volume in adaptive backstepping control method, we use the arbitrary-order robust exact differentiator to solve the high-order derivatives in feedback linearization and utilize the command filter to obtain the virtual control volume and its derivatives. The simulation results show that the robust adaptive control system we designed can achieve the error-free tracking of altitude and velocity command. It can well overcome the influence of structural parameters, aerodynamic parametric uncertainty, and disturbances; meanwhile, the control command can satisfy the constraints of the actuator.
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