In recent years, online social networks (OSNs)
have dramatically expanded in popularity around
the world. According to the data in October
2012, Facebook has 1.01 billion people using the
site each month.1 Moreover, the numbers of
users in five popular OSNs are listed in Table 1.
The rapid growth of OSNs has attracted a large
number of researchers to explore and study this
popular, ubiquitous, and large-scale service. In
this article, we focus on understanding user
behavior in OSNs.