The AS400 is well-known for its stability, security, agility, and robustness. But with the passage of time, a few of the above-mentioned parameters started showing a dip. Security took a major hit because of several circumstantial reasons, primarily because in the 80s, the AS400 was an isolated system but today, with the addition of 'i' to IBM and with the entire IT industry becoming more and more exposed to attacks, adding extra layers of security to the AS400 architecture is a no-brainer.
The weak links in the AS400 infrastructure.
Reasons why the inherent AS400 security is not enough.
Different domains of AS400 security.
Devising the AS400 security