Packet Sniffer is a method of tapping each packet as it flows across the network. It is a technique in which a user sniffs data belonging to other users of the network. It is effective on both switched networks and non-switched networks. Packet Sniffer can operate as an administrative tool or for malicious purposes. It depends on the user's intent. This Paper discusses how sniffing can be done in the case of the hub and switched network, various packet sniffer methods and different methods that AntiSniff uses to detect these sniffing programs are also discussed. A packet sniffer is a technique for monitoring network traffic. In LANs, a packet sniffer and remote network monitoring are well-known techniques used by network administrators to monitor LAN behavior and diagnose trouble.