Interesting read here for those of us (eg me) whose understanding of Linux's security advantage is still limited:

http://www.theregister.co.uk/2004/10/22/security_report_windows_vs_linux/

It's old, but I found it most illuminating - quite a long article.

Back to real life for a while - still haven't established whether Linux is still as safe as I hope it is! More googling in due course, I think.