Wheeeeeee, I just noticed the recent Register article Is Linux security a myth backs up my previous post on security of Open Source Software.
This quote sorta sums it up:
Using Linux is itself no guarantee of “security”. The same is true for all operating systems. Each platform needs to be managed actively. Bugs, viruses and other malicious threats to a system will occur. This is why it is vital that every IT system be supported with excellent management procedures to ensure its long term availability and security. Technology alone is never “secure”.