In our ongoing series on E-commerce security, we''ve focused so far on threats and vulnerabilities to commerce and computer sites in general.

We''ve looked at weaknesses, gaping holes, attacks using "Social Engineering," and we''ve seen an impressive array of hacker tools that circumvent many forms of protection that people frequently believe are secure. For those who want to catch-up with the series, here''s some links to the first three installments of "Let''s Talk about Threats..."

Installment One

Installment Two

Installment Three

Without belaboring to death the dire aspects of threats, we''ll begin to shift the focus of the series to guarding against both internal and external adversaries through conscious planning, intelligent designs, and vigilant monitoring. This week''s column looks in depth to a fundamental concept that pervades all secure Internet-accessible installations -- the three- or n-tier client-server architecture.