daSniff

daSniff is an open source customizable sniffer for win32 systems. It helps you to log your LAN traffic by specifying packet rules as filters. It has two major versions named version A and version B. Both versions use the same packet filtering, but different sniffing code. Version A uses pure WinSock2 API and runs only under Windows 2000 and above with administrator privileges. It is also available as a Windows NT service. Version B uses WinPcap as a packet capture library and runs under Windows 95/98/ME/2000/XP.