In this article, we have studied the security and privacy issues in mobile social networking and applications. We have defined MSN communication patterns, and introduced the security and privacy challenges. We have also offered several promising approaches to deal with the security and privacy challenges in various mobile applications, especially for the business card and service review applications. Lastly, we have presented three promising research directions: gestureassisted secure information sharing, social-context- based private information management, and effective resistance to mobile Sybil attacks.