Traffic volumes in mobile networks are rising and end-user needs are rapidly changing. Mobile network operators need more flexibility, lower network operating costs, faster service roll-out cycles, and new revenue sources. The 5th Generation (5G) and future networks aim to deliver ultra-fast and ultra-reliable network access capable of supporting the anticipated surge in data traffic and connected nodes in years to come. Several technologies have been developed to meet these emergent demands of future mobile networks, among these are software defined networking, network function virtualization, and cloud computing. In this paper, we discuss the security challenges these new technologies are prone to in the context of the new telecommunication paradigm. We present a multi-tier component-based security architecture to address these challenges and secure 5G software defined mobile network (SDMN), by handling security at different levels to protect the network and its users. The proposed architecture contains five components, i.e., secure communication, policy-based communication, security information and event management, security defined monitoring, and deep packet inspection components for elevated security in the control and the data planes of SDMNs. Finally, the proposed security mechanisms are validated using test bed experiments.