Energy efficiency is an essential requirement for all wireless devices. Recent developments in wireless sensor networks (WSNs), wireless local area networks (WLANs) and wireless personal area networks (WPANs) have raised a demand for energy-efficient algorithms and energy-efficient medium access control (MAC) protocols. When considering security in this context, additional overhead is added to the network and efforts must to be made to minimize the extra load while at the same time achieving the desired level of security. Security attacks in the Internet are linked to a different set of vulnerabilities. The complex architecture of the Internet spanning over different administrative domains and legal systems makes it easy for attackers to conceal the source of the attack and preserve their anonymity. This dissertation addresses several important issues in network security and performance including intrusion detection, cipher design, security overhead analysis and tracing, as follows. We first propose a model for intrusion detection in WSNs, which optimizes network coverage and detection while minimizing the number of sensors and energy consumption. We then integrate a security mechanism into the sensor network in order to achieve secure communication. Specifically, we propose a lightweight block cipher based on a multiple recursive generator (MRG) which is suitable for WSN and RFID where power consumption, bandwidth, memory and storage space are critical. Next, we consider security in WLANs and WPANs and we apply the advanced encryption standard (AES) cipher to ensure secure transmission of frames. We integrate AES encryption at the MAC layer of 802.11 WLANs and 802.15.3 UWB WPANs, respectively, and study the overhead introduced by AES in this context. Finally, we analyze a type of security attack in the Internet where the intruder uses a chain of host machines before attacking the target. We discuss two mechanisms for tracing intruders in the Internet, one based on thumbprinting, and the other on a timestamping technique of transmission activities.