Intrusion Detection - Network Security Beyond the Firewall

This book makes the case that no matter what security measures are in place, no matter how many firewalls, no matter what design of SmartCards for login, no matter what level of OS security, you still need to watch for and detect intrusions and other breaches.

The first half of the book covers security measures fully. This is a more technical treatment than Internet Security and you'd probably want at least that much background before taking up this. However, don't get scared away: this isn't really all that heavy.

The second half deals with commercial and non-commercial products that provide intrusion detection. The coverage is much more focused on the commercial products, which might be because the author works for one of the vendors mentioned.

There is a lot of good advice here for those who need to be very serious about security.