  The popularity and widespread usage of online social networks (OSN) have
attracted cyber criminals who have used OSNs as a platform to spread malware.
Among different types of malware in OSNs, Trojan is the most popular type with
hundreds of attacks on OSN users in the past few years. Trojans infecting a
user's computer have the ability to steal confidential information, install
ransomware and infect other computers in the network. Therefore, it is
important to understand propagation dynamics of Trojans in OSNs in order to
detect, contain and remove them as early as possible. In this article, we
present an analytical model to study propagation characteristics of Trojans and
factors that impact their propagation in an online social network. The proposed
model assumes all the topological characteristics of real online social
networks. Moreover, the model takes into account attacking trends of modern
Trojans, the role of anti-virus (AV) products, and security practices of OSN
users and AV software providers. By taking into account these factors, the
proposed model can accurately and realistically estimate the infection rate
caused by a Trojan malware in an OSN as well as the recovery rate of the user
population.
