During the planning of Wireless Local Area Network (WLAN) systems, it is important to determine the optimal number of access points (APs) in order to maximise their coverage with minimum cost. It is also essential to take proactive steps to secure their position in order to enhance the physical security of the network. In this paper we describe a mathematical model that finds the minimum number of APs for indoor buildings and places them in the area in a manner that the physical security of the network is maintained. A Global Optimisation Algorithm (AGOP) developed at the University of Ballarat is used to solve this problem. Results obtained demonstrate that the model and software are able to optimally solve the placement problem in areas that have different obstacles and number of users.