Mobile Cloud Computing (MCC) is a recent technology used by various people worldwide. In 2015, more than 240 million users used mobile cloud computing which earns a profit of $5.2 billion for service providers. MCC is a combination of mobile computing and cloud computing that presents various challenges like network access, elasticity, management, availability, security, privacy etc. Here, the security issues involved in both mobile computing and cloud computing, such as data security, virtualisation security, partitioning security, mobile cloud application security and mobile device security are considered extremely important. This paper presents a detailed study of security issues in mobile cloud computing and enumerates their preventive measures.