If you've read tonnes of security textbooks and are looking for a way to test them out (without actually living through a hack attack), consider Hacker's Challenge.
Designed to "test your incident response skills", Hacker's Challenge presents 20 scenarios (based on actual attacks, although company names, etc., have been changed) and their solutions. Each scenario has a narrative describing the attack - complete with date and time stamps - that reads something like a mystery novel, and then the associated logs and diagrams you need as clues. In each scenario you follow the footsteps of a fellow systems administrator or IT manager as they deal with a hack attack.
The scenarios cross industry and range in complexity, in terms of the type of attack as well as prevention and mitigation. Sometimes there are clues, but most of the time you need to go through the forensic evidence (logs, network diagrams and so on) to come to a conclusion about the attack.
Along with making Hacker's Challenge interesting reading, the scenario-based structure serves to highlight the fact that security issues cannot be addressed without considering how a company uses its network. In one scenario, for example, what looks like a hack attack (without giving too much away) turns out to stem from the way the company concerned sourced and supported its technology.
It's also refreshing to find a book that deals with securing systems without devoting pages and pages to scare mongering. There are some references to doom and gloom headlines in the introduction but, thankfully, very little tabloid-like coverage.
If your job is to secure your company's network, take a look at Hacker's Challenge - even if it's just to validate to yourself your ability to cope with an attack!