This paper addresses physical-layer security in wireless networks. We propose an efficient attack strategy for a legitimate attacker that aims to disrupt communication between illegitimate transmitter and receiver. Unlike conventional studies that assume perfect knowledge of all channel information, we consider a more realistic environment in which the attacker estimates the channel information. To this end, we apply the Least Squares (LS) channel estimation method, enabling the attacker to acquire the channel gains of eavesdropping and jamming links. Based on the estimated channel information, the attacker selects either an eavesdropping or a jamming attack at each time slot, depending on which results in higher Attacker Energy Efficiency (AEE). Simulation results demonstrate that the proposed strategy achieves highly accurate channel estimation as the signal-to-noise ratio increases and attains nearly optimal AEE.