Here's a look at the minimum security you should start with on the i5.
Make sure your QSECURITY value is set to at least 40.
Run the Print System Security Attributes (PRTSYSSECA) command to see the recommended security-related system values. Make sure that these system values are at least as restrictive as the recommendations.
Run the Analyze Default Passwords (ANZDFTPWD) command to see if any user profiles have default passwords. Change the password of any user profile that is using the default. For example, QPGMR ships with password QPGMR. Most people know this.
Use object authority to protect your important libraries and files. The i5/OS operating system has integrated object security. To access an object, the user must use the system-provided interfaces. Through these interfaces, the system ensures that the user has the correct authority to the object.