There are a number of books on the market which deal with securing Oracle.
Unfortunately, most of these books are like the sorts of survey classes you take as an undergraduate - strong on theory, light on practicality.
I decided to make it real, get rid of the fluff and like Linus Torvalds said "Talk is cheap, show me the code!" (He invented the Linux OS).
I list the things you should do, the reasons you should do these things, and I also provide you with the code to automate as many of these security recommendations as possible.
Installing and Configuring Bugzilla Using Oracle on Windows Published January 26, 2009
Hunting the Diamond Doggerel Published August 10, 2008