This is an excellent paper that goes into some great detail on latches. There are some internal looks at X$ tables and also some examples of use of oradebug. The paper covers "what is an Oracle latch", latches and enqueues, Oracle latch internals, how processes sleep/wakeup mechanism is working for the process waiting in latch, latch contention identification and finally problems with latches.
This is a good paper and very detailed. It is not about security but I liked it because of its internals and detailed information.