<div>ABSTRACT</div><div><br></div><div>Primary User Emulation Attack (PUEA) is one of the major threats to the spectrum sensing in cognitive radio networks. This paper studies the PUEA using energy detection that is based on the energy of the received signal. It discusses the impact of increasing the number of attackers on the performance of secondary user. Moreover, studying how the malicious user can emulate the Primary User (PU) signal is made. This is the first analytical method to study PUEA under a different number of attackers. The detection of the PUEA increases with increasing the number of attackers and decreases when changing the channel from lognormal to Rayleigh fading.</div><div><br></div><div>KEYWORDS:</div><div><br></div><div>Cognitive Radio, Primary User Emulation Attacks (PUEA), energy detector.</div