[throwaway7356]

> I saw years of uptime on those systems

This just means security updates were never installed.

(Or you claim that all those operating systems never had kernel-level security issues which seems doubtful...)

[cobbaut]

Since these systems were from the 90ies they indeed did not get security updates.

Most were only locally connected (for example OS/2 had a Token Ring in one building). The WAN connection (for AS/400) was trusted.