Network security has always been a large concern and is more important than ever with the increasing usage of Wireless Ad Hoc Networks, otherwise known as MANETs. Due to its usage of dynamic node topology, MANETs today are severely unprotected from attacks and threats from malicious nodes. This research aims to study the impact of attacks on the performance of MANETs with the use of the QualNet Simulator to simulate the data link layer and network layer in a MANET. Both passive and active attacks will be investigated in this research, eavesdropping and wormhole attacks respectively to be specific. The performance of a MANET prior to and during an attack will be measured and recorded. The recorded output will be analyzed and compared against each other to determine the impact of the attacks on the network. "What-if" analyses are also executed to achieve results that closely simulate those of the real world.