His main thesis was basically that every
OS in common use today, from Windows to UNIX variants, has a fundamental
flaw in the way privileges and permissions are handled - the concept of
superuser/administrator. He argued instead that OSes should be
implement the principle of least privilege from the ground up, down to
architecture they run on. OpenSSH's PrivSep (now making its way into
daemons in the OpenBSD tree) is a step in the right direction.
Capability-based systems like EROS-OS are a way of addressing this issue.
Have a look at http://www.eros-os.org/
If you only read one article then pick this summary from IEEE Software
The slammer worm made its way into some very unexpected places. It seems
that in many organizations, once the UDP packet made its way to one MS-SQL
server through one hole, it then acquired all the privileges of the IP
address that supposedly belonged to a database server. Since traffic from
the database server was considered to be trustworthy, it was able to
easily reach and infect many more internal MS-SQL servers that were on
internal networks unconnected to the Internet. In other words, there were
MS-SQL servers acting as Application Layer Gateways to transport the worm
into protected networks.
The random nature of the addresses chosen by the worm virtually guaranteed
that every single network path in the world containing MS-SQL servers
would be infected.