The primary issue with respect to securing Mobile Ad hoc NETworks (MANETs) is that of ensuring network integrity even when the network is subject to attacks to break its connectivity. In this research report, we study how to secure the OLSR routing protocol . We first analyse the attacks that can be launched against the network integrity. We then present mechanisms for ensuring that only ``trusted'' nodes are admitted into the network and, subsequently, are the only nodes used to forward traffic. We also present mechanisms for detecting and dealing with scenarios where ``trusted'' nodes have become compromised.