Toad Pocket Reference for Oracle Book

This book covers security at Many different levels (tries to be comprehensive)... although this is a constantly changing topic of study, every time new tactics are used by some hacker/virus/trojan...etc.

Topic included are: the "Meaning of Computer Security", Attacks & methods of defense, cryptology, software(code) security, Viruses, root-hacks, Operating system security, Trusted-systems, File protections, Database security, SQL injection, Multi-Level approaches, Networks, firewalls, Vlans, Session hijacking, flaws in net protocols, Web site vulnerabilities, Alarms, monitoring, countermeasures, Administration, Risk Analysis, Physical building security, Data privacy, computer ethics, Email monitoring or interception, spoofing, phishing, computer crime, code of ethics, SOA Architecture, and more...

This is certainly not a "light read" or something you complete in a week; but for somebody who runs computers professionally, there is a lot of info here -so you know several problem issues to avoid when designing new computer systems.

I would also recommend knowing the ISO-27001 and ISO-27009 standards, and similar security standards from OWASP (Open.Web.Application.Security.Project),
plus Oasis-open.org guides.