In recent years, research on social networks has progressed considerably. The emergence of social websites, e-mails, telephone diaries and instant messaging has greatly influenced the development of sophisticated techniques for analysing these networks, using graph theory and machine learning in particular. Increasingly, web users see the web as a social medium that encourages interaction, the sharing of experience and knowledge, and the formation and evolution of communities. This evolution has led to a significant increase in social network analysis in various spheres such as academia, politics, homeland security and business.