The boost in the use of wireless networks in our day-to-day world is phenomenal. Users need to have a confidence in communicating securely over the wireless medium. They want to be able to trust in the genuineness of a transmitting node. In this work, we examine an attack, called the evil-twin transmitter attack. In a wireless network comprising some receivers and a truth-teller transmitter, an attacker adds a malicious evil-twin transmitter to the network such that the evil-twin lies about its true identity and transmits like the truth-teller transmitter in the network. The truth-teller transmitter may be a malicious transmitter as well, but it is honest in that it doesn't lie about its identity. The evil-twin uses the identity of the truth teller and transmits at the same time as the truth-teller. The receivers are bound to get confused about the location of the honest transmitter. We have described an algorithm to detect the wireless evil-twin transmitter attack as well as to localize the two transmitters. Our contributions with this work are: 1. We have simulated the use of directional antennas for determining whether a wireless network is under an evil-twin transmitter attack. The algorithm for detecting an evil-twin transmitter attack can be used independently, as well as in conjunction with a localization technique, depending on the problem scenario. 2. The previously devised Hyperbolic Position Bounding (HPB) mechanism is used to localize the two transmitters. We have also provided an alternative mechanism to localize the transmitter in case HPB fails to localize the transmitter. The performance of the algorithm is tested using a simulation of a wireless network, the results of which are consistent over various scenarios. Directions for future work include determining which of the two transmitters is the truth-teller and the evil-twin.