Even though he had sealed up all the holes he knew about, Tom still wanted to know if there was unusual activity happening on his LAN or against his public IP addresses. He used a network sniffer called Ethereal to establish a baseline for different types of activity on his network (Chapter 6). He also set up a Network Intrusion Detection System (NIDS) on a server, using a software package called Snort (Chapter 7). This program watched his network 24/7, looking for suspicious activity that Tom could define specifically , telling him if new attacks were happening, and if people on the inside were doing something they shouldn't be.
