How Secure are security policies?

Suppose I have an application instrumented using MBeans, and those Mbeans contain sensitive information. I know that you can write policy files to grant permissions to grant/deny access to MBean attributes and operations, but just writing policy files does not seem to be too secure. How can I make it more secure. I am very new to JAVA security BTW.

[357 byte] By [AUTOMATONa] at [2007-11-26 20:08:00]